"the file could not be loaded into the web forms"

[Randy]

Hello,
Me and another guy are working on an ASP c# project. We're using Vault for
source control.
I originally started on a form and then let him develop it (I didn't give
him my aspx, cs or resx), he developed it on his own.
Later, I got a form (aspx, cs.resx) from him (downloaded it from Vault). Now
when I try and open the aspx file I get the above error. I've check ed the
@Page and Codebehind attributes and they look fine.
Is there a way to correct this?

Thanks