I found that once upon a time this machine had been infected with this. Somehow it had registered itself with Windows Security Center thus was still showing as an installed antivirus package. Funny thing too, it said it was current on its virus definitions.
To correct this I issued the following commands from a CMD prompt on that PC:
net stop winmgmt
cd /d %windir%\system32\wbem
ren repository repository.old
net start winmgmt
As I understand it, if you had an issue where no antivirus package was being found by Windows Security Center, the above commands might work for that too.
After issuing the above commands, I forced Spiceworks to rescan and it correctly identified that just Symantec Endpoint was installed.