Visual Studio 2005 and .NET 2.0 brought many new features to ASP.NET 2.0, many great, but some that down right stunk. One of the best and worst features was the compilation model that allowed for per page compiling and the removal of needing namespaces for pages. It was a noble idea, but the implementation left MUCH to be desired. One of the biggests loses because of the change was that it was VERY difficult to create web pages that were derived from anything other that System.Web.UI.Page, unless they were in the App_Code directory.
Fortunately with the re-introduction of Web Application Projects, the web pages went back to being more developer friendly. Now, one can create a class derived from System.Web.UI.Page anywhere, and the Web pages will now recognize the classes correctly. The only issue I have run across is that the html/design surface is NOT derived, so, one cannot just place a button on a base form (.aspx file), and expect to have it displayed on a derived page.
I should have posted this a LONG time ago (ie, when the ORIGINAL solution came out), but I not had a need to work with it until now. Hopefully this will get the word out that we can go back to using derived web pages again!