Hi I've not had the time to dedicate to looking at this problem until now.  After reading the through the forums I found somebody else who was having the same issue as me, as a site collection admin I am able to see the chart but site contributers are not able to see the chart.  So after finding that they had resolved their issue by installing the latest beta, I did the same.  However, now I am completely unable to group by the month in a date field.  I get a huge error when I go to the debug window. 
  
Debug Information: 
Renderer: Flash
Flash Player installed: true
Browser Information: 
App code name: Mozilla
App name: Microsoft Internet Explorer
Version: 4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)
Platform: Win32
User agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)
Invoker: Error message
SharePoint Version: 14.0.6134.5001
ErrorLog entries: 
Date: 07/06/2013 09:08:27
Title: Chart preview could not be generated. Please check your chart settings and try again.
Chart Version: 1.1.2.0
Exception Method: GetChartXmlPreview
Exception: Chart preview could not be generated. Please check your chart settings and try again.
Type: Error
Stack Trace:    at Collabion.Charts.Business.Helpers.DataTableHelper.ApplyGroupBy(DataTable sourceTable, GroupByOperation groupBy, ChartConfiguration chartConfiguration)
   at Collabion.Charts.Business.Providers.ListDataProvider.<>c__DisplayClassf.<GetDataFromStorage>b__9()
   at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass4.<RunWithElevatedPrivileges>b__2()
   at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)
   at Collabion.Charts.Business.Providers.ListDataProvider.GetDataFromStorage(ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.Providers.Base.DataProviderBase.GetData(ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.ChartBuilder.GetData(IDataProvider provider, ChartConfiguration configuration, Boolean preview, String IsDynamicFilter, String drillLimit, String DatasetIndex, String DrillDownTitle)
   at Collabion.Charts.Business.ChartBuilder.GetXml(ChartConfiguration configuration, IDataProvider provider, Boolean preview, String IsDynamicFilter, String drillLimit, String DatasetIndex, String DrillDownTitle)
   at Collabion.Charts.Business.ChartBuilder.GetXml(ChartConfiguration configuration, Boolean preview, String IsDynamicFilter)
   at Collabion.Charts.WebServicePage.OnInit(EventArgs e)
Inner Stack Trace: 
Inner Exception: 
Additional Information: 
Request: http://myserver/_layouts/CollabionCharts/WebService.aspx
----------------------------------------------------------------------------------
Date: 07/06/2013 09:08:27
Title: Data from the selected data source could not be retrieved. Please check your connection settings and try again.
Chart Version: 1.1.2.0
Exception Method: GetData
Exception: Item does not exist.
The page you selected contains an item that does not exist.  It may have been deleted by another user.
Type: Error
Stack Trace:    at Microsoft.SharePoint.SPGlobal.HandleComException(COMException comEx)
   at Microsoft.SharePoint.Library.SPRequest.DeleteItem(String bstrUrl, String bstrListName, Int32 lID, UInt32 dwDeleteOp, Guid& pgDeleteTransactionId)
   at Microsoft.SharePoint.SPListItem.DeleteCore(DeleteOp deleteOp)
   at Microsoft.SharePoint.SPListItem.Delete()
   at Collabion.Charts.DAL.ListHelper.DeleteItems(SPWeb web, String listTitle, SPQuery query)
   at Collabion.Charts.DAL.Managers.DataManager.DeleteItems(String primaryKeyName, Int32 primaryKeyValue)
   at Collabion.Charts.DAL.Managers.DataSetManager.SaveDataSets(Int32 configurationId, IList`1 dataSets)
   at Collabion.Charts.Business.Providers.ListDataProvider.ProcessCalculatedColumns(DataTable table)
   at Collabion.Charts.Business.Providers.ListDataProvider.<>c__DisplayClass25.<GetDataFromStorage>b__1f()
   at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass4.<RunWithElevatedPrivileges>b__2()
   at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)
   at Collabion.Charts.Business.Providers.ListDataProvider.GetDataFromStorage(Boolean includeFiltering, Boolean includeGrouping, Boolean includeSelectedFields, ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.WebService.GetData(String webPartId, String name, String configurationStep, String startRecord, String recordsLimit, String IsDynamicFilter, String HotspotWebPartId)
   at Collabion.Charts.WebServicePage.OnInit(EventArgs e)
Inner Stack Trace:    at Microsoft.SharePoint.Library.SPRequestInternalClass.DeleteItem(String bstrUrl, String bstrListName, Int32 lID, UInt32 dwDeleteOp, Guid& pgDeleteTransactionId)
   at Microsoft.SharePoint.Library.SPRequest.DeleteItem(String bstrUrl, String bstrListName, Int32 lID, UInt32 dwDeleteOp, Guid& pgDeleteTransactionId)
Inner Exception: Item does not exist.
The page you selected contains an item that does not exist.  It may have been deleted by another user.
Additional Information: 
Request: http://myserver/_layouts/CollabionCharts/WebService.aspx
Chart Configuration: 
   WebPartId: g_bcf1756c_27b3_45cb_a405_5b64bfac6964
   Settings: {"chart":{"data":null,"_previewanimation":1,"_exportenabled":1,"_exportatclient":0,"_exportshowmenuitem":1,"_exporthandler":"/_layouts/CollabionCharts/FCExporter.aspx","_html5exporthandler":"/_layouts/CollabionCharts/FCJSExporter.aspx","_exportcallback":"CC_onAfterExportObjectSaving","_exportaction":"download","_exportfilename":"Collabion Charts","_aboutmenuitemlabel":"About Collabion Charts","_aboutmenuitemlink":"n-http://www.collabion.com/","_showsecondarylimits":1,"_showdivlinesecondaryvalue":1,"_animation":1}}
   Height: 460
   Width: 400
   Type: 14
   ProviderName: g_bcf1756c_27b3_45cb_a405_5b64bfac6964
   CategoriesColumnName: Start_x0020_Date
   CategoriesAttributes: 
   CategoriesSort: 
   CategoriesDateDisplayFormat: dd/MM/yyyy
   Messages: 
   BatchMode: False
   IsFlashRender: True
   DrillDownSort: 
   DrillDownGroupBy: 
   DrillDownFunction: -1
   GroupDatesBy: 0
Provider Configuration: 
   WebPartId: g_bcf1756c_27b3_45cb_a405_5b64bfac6964
   ProviderType: 0
   Entity: ebdfa1d7-ff1d-4aa4-936d-5afe3ddee3d5
   View: dc2236a6-bd6f-4344-83d2-ac003de5bfcc
   ViewFields: Start_x0020_Date,Course_x0020_Price,Financial_x0020_Year,
   GroupByColumnName: Start_x0020_Date
   SplitByColumnName: 
   GroupDatesBy: 3
   FilterGroupDateType: 0
   FilterGroupDateValue: 
   Query: 
   QueryVariables: 
   IsEncrypted: True
----------------------------------------------------------------------------------
Date: 07/06/2013 09:07:52
Title: Chart preview could not be generated. Please check your chart settings and try again.
Chart Version: 1.1.2.0
Exception Method: GetData
Exception: Chart preview could not be generated. Please check your chart settings and try again.
Type: Error
Stack Trace:    at Collabion.Charts.Business.Helpers.DataTableHelper.ApplyGroupBy(DataTable sourceTable, GroupByOperation groupBy, ChartConfiguration chartConfiguration)
   at Collabion.Charts.Business.Providers.ListDataProvider.<>c__DisplayClass25.<GetDataFromStorage>b__1f()
   at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass4.<RunWithElevatedPrivileges>b__2()
   at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)
   at Collabion.Charts.Business.Providers.ListDataProvider.GetDataFromStorage(Boolean includeFiltering, Boolean includeGrouping, Boolean includeSelectedFields, ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.WebService.GetData(String webPartId, String name, String configurationStep, String startRecord, String recordsLimit, String IsDynamicFilter, String HotspotWebPartId)
   at Collabion.Charts.WebServicePage.OnInit(EventArgs e)
Inner Stack Trace: 
Inner Exception: 
Additional Information: 
Request: http://myserver/_layouts/CollabionCharts/WebService.aspx
Chart Configuration: 
   WebPartId: g_bcf1756c_27b3_45cb_a405_5b64bfac6964
   Settings: {"chart":{"data":null,"_previewanimation":1,"_exportenabled":1,"_exportatclient":0,"_exportshowmenuitem":1,"_exporthandler":"/_layouts/CollabionCharts/FCExporter.aspx","_html5exporthandler":"/_layouts/CollabionCharts/FCJSExporter.aspx","_exportcallback":"CC_onAfterExportObjectSaving","_exportaction":"download","_exportfilename":"Collabion Charts","_aboutmenuitemlabel":"About Collabion Charts","_aboutmenuitemlink":"n-http://www.collabion.com/","_showsecondarylimits":1,"_showdivlinesecondaryvalue":1,"_animation":1}}
   Height: 460
   Width: 400
   Type: 14
   ProviderName: g_bcf1756c_27b3_45cb_a405_5b64bfac6964
   CategoriesColumnName: Start_x0020_Date
   CategoriesAttributes: 
   CategoriesSort: 
   CategoriesDateDisplayFormat: dd/MM/yyyy
   Messages: 
   BatchMode: False
   IsFlashRender: True
   DrillDownSort: 
   DrillDownGroupBy: 
   DrillDownFunction: -1
   GroupDatesBy: 0
----------------------------------------------------------------------------------
Date: 07/06/2013 09:07:52
Title: Chart preview could not be generated. Please check your chart settings and try again.
Chart Version: 1.1.2.0
Exception Method: GetChartXmlPreview
Exception: Chart preview could not be generated. Please check your chart settings and try again.
Type: Error
Stack Trace:    at Collabion.Charts.Business.Helpers.DataTableHelper.ApplyGroupBy(DataTable sourceTable, GroupByOperation groupBy, ChartConfiguration chartConfiguration)
   at Collabion.Charts.Business.Providers.ListDataProvider.<>c__DisplayClassf.<GetDataFromStorage>b__9()
   at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass4.<RunWithElevatedPrivileges>b__2()
   at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)
   at Collabion.Charts.Business.Providers.ListDataProvider.GetDataFromStorage(ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.Providers.Base.DataProviderBase.GetData(ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.ChartBuilder.GetData(IDataProvider provider, ChartConfiguration configuration, Boolean preview, String IsDynamicFilter, String drillLimit, String DatasetIndex, String DrillDownTitle)
   at Collabion.Charts.Business.ChartBuilder.GetXml(ChartConfiguration configuration, IDataProvider provider, Boolean preview, String IsDynamicFilter, String drillLimit, String DatasetIndex, String DrillDownTitle)
   at Collabion.Charts.Business.ChartBuilder.GetXml(ChartConfiguration configuration, Boolean preview, String IsDynamicFilter)
   at Collabion.Charts.WebServicePage.OnInit(EventArgs e)
Inner Stack Trace: 
Inner Exception: 
Additional Information: 
Request: http://myserver/_layouts/CollabionCharts/WebService.aspx
----------------------------------------------------------------------------------
Date: 07/06/2013 09:07:41
Title: The chart preview could not be generated. Please check your connection settings. Additionally, please revert your last changes to chart settings and try again.
Chart Version: 1.1.2.0
Exception Method: GetChartXmlPreview
Exception: Item does not exist.
The page you selected contains an item that does not exist.  It may have been deleted by another user.
Type: Error
Stack Trace:    at Microsoft.SharePoint.SPGlobal.HandleComException(COMException comEx)
   at Microsoft.SharePoint.Library.SPRequest.DeleteItem(String bstrUrl, String bstrListName, Int32 lID, UInt32 dwDeleteOp, Guid& pgDeleteTransactionId)
   at Microsoft.SharePoint.SPListItem.DeleteCore(DeleteOp deleteOp)
   at Microsoft.SharePoint.SPListItem.Delete()
   at Collabion.Charts.DAL.ListHelper.DeleteItems(SPWeb web, String listTitle, SPQuery query)
   at Collabion.Charts.DAL.Managers.DataManager.DeleteItems(String primaryKeyName, Int32 primaryKeyValue)
   at Collabion.Charts.DAL.Managers.DataSetManager.SaveDataSets(Int32 configurationId, IList`1 dataSets)
   at Collabion.Charts.Business.Providers.ListDataProvider.ProcessCalculatedColumns(DataTable table)
   at Collabion.Charts.Business.Providers.ListDataProvider.<>c__DisplayClassf.<GetDataFromStorage>b__9()
   at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass4.<RunWithElevatedPrivileges>b__2()
   at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param)
   at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode)
   at Collabion.Charts.Business.Providers.ListDataProvider.GetDataFromStorage(ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.Providers.Base.DataProviderBase.GetData(ChartConfiguration ChartConfiguration)
   at Collabion.Charts.Business.ChartBuilder.GetData(IDataProvider provider, ChartConfiguration configuration, Boolean preview, String IsDynamicFilter, String drillLimit, String DatasetIndex, String DrillDownTitle)
   at Collabion.Charts.Business.ChartBuilder.GetXml(ChartConfiguration configuration, IDataProvider provider, Boolean preview, String IsDynamicFilter, String drillLimit, String DatasetIndex, String DrillDownTitle)
   at Collabion.Charts.Business.ChartBuilder.GetXml(ChartConfiguration configuration, Boolean preview, String IsDynamicFilter)
   at Collabion.Charts.WebServicePage.OnInit(EventArgs e)
Inner Stack Trace:    at Microsoft.SharePoint.Library.SPRequestInternalClass.DeleteItem(String bstrUrl, String bstrListName, Int32 lID, UInt32 dwDeleteOp, Guid& pgDeleteTransactionId)
   at Microsoft.SharePoint.Library.SPRequest.DeleteItem(String bstrUrl, String bstrListName, Int32 lID, UInt32 dwDeleteOp, Guid& pgDeleteTransactionId)
Inner Exception: Item does not exist.
The page you selected contains an item that does not exist.  It may have been deleted by another user.
Additional Information: 
Request: http://myserver/_layouts/CollabionCharts/WebService.aspx
----------------------------------------------------------------------------------
Operating System Details
OS Version: 6.1.7601.65536
OS Platform: Win32NT
OS ServicePack: Service Pack 1
OS Version String: Microsoft Windows NT 6.1.7601 Service Pack 1