Interesting...my web app wouldn't build and was griping about my .designer.cs file beneath a Master PAge. Everything looked fine and should work. I had run ReSharper optimize usings command and it optimized...but the page wanted the fully qualified name on the field (control) entry...strange that it would require that. Oh well.
[UPDATE]: using the optimize usings command in Resharper on the WebPages screws everything up for me...note to self: DON'T DO THAT.