Hi,
Is there any update on this? I'm experiencing the same problem with XT - 'Invalid Argument' when in IE8 non compatibility mode, but works when IE is in compatibility mode.
Strangely enough I can workaround this by adding the line "Response.Write(xmlData.ToString())" just before the RenderChart command, although I have no idea why or how this should work!
Cheers,
Paul.