The subject error occurs for certain application, like a terminal services client, on your Windows 2000 Professional workstation.
This behavior occurs if you installed Windows XP themes, and the Windows XP uxtheme.dll file was copied to your %SystemRoot%\System32 folder.
NOTE: The %SystemRoot%\System32\uxtheme.dll file is in use and cannot be deleted or unregistered.
To resolve this problem:
1. If %SystemRoot%\System32\DLLCACHE\uxtheme.dll exists, rename it to %SystemRoot%\System32\DLLCACHE\uxtheme.CFG.
2. Rename %SystemRoot%\System32\uxtheme.dll to %SystemRoot%\System32\uxtheme.cfg.
3. Shutdown and restart Windows 2000.
4. if the %SystemRoot%\System32\DLLCACHE\uxtheme.cfg file exists, delete it.
5. Delete the %SystemRoot%\System32\uxtheme.cfg file.