Make sure that you are using Microsoft AntiSpyware under
an account logged in with Administrator rights.
If that doesn't fix it, then:
1. Uninstall Microsoft AntiSpyware
2. Delete the directory
C:\Program Files\Microsoft AntiSpyware
3. Run Windows Explorer, go to your profile temporary
folders (usually C:\Documents and Settings\username\local
settings\temp and c:\Documents and Settings\username\local
settings\Temporary Internet Files\Content.IE5) and delete
all the files in those directories and subdirectories.
Then do a full system scan with MS AntiSpyware (check the
proper option under Scan settings). Scan the computer with
the antivirus software that you use.
4.Re-install Microsoft AntiSpyware.