If you receive the subject message when opening or exploring a folder, chances are that you installed IE 4.x, including the Windows Desktop Update, and the DesktopProcess key was already present in the registry.

To resolve the problem, use Regedt32 to navigate to:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer

and delete the DesktopProcess key.

Shutdown and restart Windows NT.