After the last round of MS security patches, my computer gave the following error message after boot:
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.
Microsoft has released a hotfix for this issue (designated KB935448), apparently caused by an incompatibility between the above security hotfixes and RealTek’s audio HD control panel.