A number of people have been receiving the following error recently when starting Windows:

RTHDCPL. EXE - Illegal system DLL relocation. the system DLL user 32. dll was relocated in memory. the application will not run properly. the relocation occured because the DLL C:/WINDOWS/system32/HHCTRLOCX occupied an address range reserved for Windows system DLLs. the vendor supplying the DLL should be contacted for a new DLL.

Just a bit of reassurance, there is nothing illegal about this file. It basically means a couple of files are trying to talk to each other but due to a change in one of both some applications may not work

According to the Microsoft web site this was possibly caused by a recent Windows update.

"This problem may occur after you install security update 925902 (MS07-017) and security update 928843 (MS07-008). The Hhctrl.ocx file that is included in security update 928843 and the User32.dll file that is included in security update 925902 have conflicting base addresses. This problem occurs if the program loads the Hhctrl.ocx file before it loads the User32.dll file."

Details of the Microsoft Security Bulletin MS07-017

Details of how Microsoft suggest you resolve the issue can be found in Article 935448.