Whilst not labeled as incompatible I notice that Paretologic's website has a red warning from at least one web security firm, WoT. Registry cleaners and optimizers which are Paretologic's speciality it seems, are guaranteed to eventually screw up your system and most definitely the McAfee software.
Believe me, they are bad news.
If you want anti-malware that is acceptable see the last link in my signature below, under '3rd Party Tools'.
Can you open McAfee SecurityCenter and does it say it's green and protecting?
It probably doesn't run a scan because at some stage you turned off that feature. You can check that under Virus and Spyware Protection > Scheduled Scans.