You need to be sure that the VirusScan item in the master repository really is the actual install set (should be easy to work out, but you do need to read the detail in the columns.)
You need to ensure that the VirusScan extensions have also been installed.
You'll know if the extensions are missing because so will all the VirusScan policies in the policy catalog.
This McAfee article was written for ePO 4.0, but the principles are similar as far as extensions installation go, so you'll get the idea:
KB53916 - How to check the VSE 8.7i installation package and extensions into ePO 4.0