I have always found Windows Active Desktop to be a very heavy and unnecessary feature. Sometimes, you find that you can't disable it using the usual methods. There is another way to force-disable/enable the active desktop.
Create a new DWORD value named "NoActiveDesktop", and set the new value to equal "1" to enable the restriction or "0" to disable the restriction.
This restriction can be used either on a user by user basis by adding it to HKEY_CURRENT_USER or on a computer wide basis by adding it to HKEY_LOCAL_MACHINE.
User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
System Key: [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
Value Name: NoActiveDesktop
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disable restriction, 1 = enable restriction)
Disclaimer: Modifying the registry can cause serious problems that may require you to reinstall your operating system. We cannot guarantee that problems resulting from modifications to the registry can be solved. Use the information provided at your own risk.