System Error &h80070002&

I upgraded a VS 2003 web application to VS 2010.

I had to sort out a whole range of errors.

When I compile now I get the following error message:

'Unable to open file C:\inetpub\wwwroot\Project\obj\Release\Project.Report..aspx.resources: System Error &h80070002&'

If I Clean the Project this error disappears but when I try to run it or build it again I get the error message again.

Anyone know why I'm getting this error?

Thanks.