Microsoft recently issued security updates (for the Windows XP operating system) where one delivered DLL loaded to an address range in conflict with another DLL. From the failed updates, a warning emits:

Rthdcpl.exe - Illegal System DLL Relocation

The system DLL user32.dll was relocated in memory. The application will not run properly. The relocation occurred because the DLL C:\Windows\System32\Hhctrl.ocx occupied an address range reserved for Windows system DLLs. The vendor supplying the DLL should be contacted for a new DLL.

Two security updates precipitate this failure. The first update was 925902 to guard against remote code execution via GDI. The second update was 928843 to guard against remote code execution via HTML. More detail of this conflict is available in the Microsoft Knowledge Base; concerned users should read this specific article.