I got this message at start-up on Windows XP after a security update was installed:

The system DLL user32.dll was relocated in memory. the application will not run properly. the relocation occured because the DLL C:\windows\system32\hhctrl.ocx occupied an address range reserved for windows systems DLLs. the vendor supplying the DLL should be contacted for a new DLL

To correct the error, just visit this page at Microsoft and download the patch listed.