Getting the above errror while changing the theme of the XamRibbon using the following code:
this.xamRibbon.Theme = radioButton.Tag.ToString();
where the radioButton's tag property contains the theme values like "Office2k7Black", "Office2k7Blue" etc.
This problem does not occur in the samples where the Theme is being set so I suspect you must have a style that has OverridesDefaultStyle set to true. Can you post a sample that demonstrates the problem? Perhaps your issue is similar to the one discussed here - http://forums.infragistics.com/forums/t/2549.aspx - where someone had set this property in their tooltip style?
Thanks Andrew for the reply. There was problem in the styles that I was using. Particularly the OverridesDefaultStyles was being set to True.