While working on updating our NFM Printer Driver, I started running into an RC2144 error (PRIMARY LANGUAGE ID not a number). After looking and looking to no avail, it appears that there is a flaw in Visual Studio 2010 Service Pack 1 (at least, that is the first time I noticed this issue). If you edit your resources using the WYSIWYG resource editor, Visual Studio forgets to include windows.h in the rc file that it recreates when you save your changes.
You can fix it by adding the include for windows.h back into your rc file with a text editor to fix it. Add it right before the include for you resource.h file, like so:
// Microsoft Visual C++ generated resource script.
//
#include <windows.h>
#include "resource.h"
Hopefully, this will save someone else a little time.