Is your codebehind file associated with your .aspx file? If you enable Show All Files you should be able to expand the .aspx file to see the .cs file in solution explorer.

>A consultant just sent me some ASPX pages (along with the .CS and .RESX files). I unzipped them into my project folder with the ASPX pages that I developed. After adding them using the "Add existing item", then compiling them, I get the following error for each of the pages. The consultant says the pages work fine on his system. Any idea what the problem is?