Try deleting the user option files for the projects and solution. Delete all obj and bin folders. More importantly, clear out the temporary files.
Using Visual Studio 2008 temporary files, for example:
- ("%APPDATA%") & "\Microsoft\VisualStudio\9.0\ProjectAssemblies")
- ("%USERPROFILE%") & "\Local Settings\Application Data\ApplicationHistory")
- ("%USERPROFILE%") & "\Local Settings\Application Data\Microsoft\VisualStudio\9.0\ProjectAssemblies")
- ("%WINDIR%") & "\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files")