I had a similar problem after installing Norton Antivirus 2007. I
still had some remnants left over from my previous version.
What I did to fix it:
Ran the Norton Removal Tool to uninstall Norton Antivirus
Re-booted in safe mode
Deleted Symantec directory under Documents and Settings
Deleted Symantec Shared directory under Program Files\Common Files
Ran the Issues tool within CCleaner several times to clear out obsolete
registry entries
Re-booted
Re-installed Norton Antivirus 2007