Moved to VirusScan Other for better attention.
Please make sure that there are no remnants of the files from the other Antivirus.
Reboot the system and then try again and see if it is successful.
If you continue to have problems, Please call up the McAfee Support line at 1 866 622 3911.
This person is in Mexico Sameer.
I used CleanMyMac to get rid of the applications then I searched for other files in user/Library/Preferences. From what I have researched these are the only two files that would be left after uninstalling iantivirus, either using CleanMyMac or the provided uninstaller