Error message (Visual Studio 2003):

An unhandled exception of type 'System.Resources.MissingManifestResourceException' occurred in mscorlib.dll

Could not find any resources appropriate for the specified culture (or the neutral culture) in the given assembly.
Make sure "<YourControl>.resources" was correctly embedded or linked into assembly "<YourAssembly>".

Renaming a namespace caused this problem.
To solve this, check the namespaces of  files in your project and check the default namespace in Solution Explorer, Project, Properties.
 

Other situations might cause the same problem, see http://support.microsoft.com/default.aspx?scid=kb;en-us;318603