VS 2010 RC Patch available for the # 1 Connect bug
The most commonly reported/voted for Connect bugs in the Release candidate had to do with the ASP.NET designer not auto generating controls properly – it would sometimes just omit them. Very frustrating if you are trying to use it. We’ve just release a patch (the 3rd RC patch in total) to address this set of issues. You can read more about the patch here: http://blogs.msdn.com/webdevtools/archive/2010/03/05/hotfix-for-issue-with-auto-generated-designer-files-not-adding-controls.aspx
And you can download and install it here: http://connect.microsoft.com/VisualStudio/Downloads/DownloadDetails.aspx?DownloadID=27117
Hopefully this will address this issue and get you moving forward again.