Hi Laurence,
Did you install the mojoportal package for .NET 4?
Make sure you do use the .NET 4 package and make sure you use the new Web.config file not your old one.
Do you have any custom features installed that depend on the AjaxControlToolkit? If so you need to re-compile them against the newer version of AjaxControlToolkit that is included in mojoPortal.
Please ask one question per thread so that thread titles match the question, it makes things easier to find.
Best,
Joe