Yeah, I get the inheritance. The prob is that neither the base nor derived classes have Profile & ApplicationInstance as members. The only idea I have is that the .net UserControl class that the base class derives from has changed to include these members & require them to be overridden (which I believe means they would have to be marked as "abstract"?). I'm not certain if this I the case, but without changing the code when upgrading to .net 4, these warnings now appear. - O8