>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.

>
>Also why do I need Windows Form in a WEB application?

I've noticed that as well, but I've never had time to investigate it.

>
>Do you know how can I copy the references and their versions, BTW? This dialog doesn't seem to allow copy them.
>

Sorry, no.