>>>They both are 3.5.0 already. However, several other references are 2.0 Should I try to update them? >> >>No, that shouldn't be necessary. Most of the other references haven't been updated to a 3.5-specific version. >> >>Did you upgrade the AjaxControlToolkit as well? If not, that's probably the source of your error. >> > >How exactly should I update it? I thought everything is included with the installation. > >The version says BIN AutoUpdate.
There is a different version required for VS 2008/3.5:
