PC Tools Spyware Doctor is an appreciated and awarded antispyware: there exist a commercial version and a free Starter Edition (with less features) available with Google Pack.
If you use the commercial version and your license ended even uninstalling SD you won't be able to install and use Starter Edition cause its license information remains hidden in the Windows Registry and there is no way to delete it.
In order to fix this issue PC Tools made availble a Spyware Doctor Reset Key, simply download it
Code:
http://support.pctools.com/manager/downloads.php?file=SpywareDoctorReset.exe
and execute.
If you get an error, download this DLL
Code:
http://support.pctools.com/manager/downloads.php?file=ArmAccess.dll
and copy into C:\Windows\System32 folder
That's all.
WARNING: a different use of this tool is forbidden