Hi,
if you are setting styleSheetTheme in web.config, then remove it and set it in you page in stead.
Thats what I did to resolve Object error in asp.net 2.0.
Change for instance:
<pages styleSheetTheme="theme1">
to:
<pages>
Set this in top of your page:
EnableTheming="true" Theme="theme1" StylesheetTheme="theme1"