bug

We have a dashboard view, where we have to update a chart on screen every 30 seconds. We do this via an AJAX call to get the latest data and then call setXMLData to refresh the chart. It works for a couple of days, but then stops re-drawing the chart. The strange thing is that the chart refreshes as soon as you move the cursor over the chart. There are no javascript errors, the data is correct, it simply stops refreshing the chart on screen. Has anyone seen this before? I would really appreciate any pointers on where to look or what to change. Thank you!