Indeed you have solved your own question

2 A/V programs built for the same Purpose can see each other as "enemies" and If they don't "fight" they'll cancel each other out leaving you with little protection
the same is True with firewalls Have 2 on board then they block nearly everything or open a door to a "nasty"

The Normal Practice is to turn off Windows Firewall and put your firewall as the main Firewall,and if that fails, or is turned off? Windows firewall steps in (as a weak Backup)
Returning to your 2 A/V Programs I'd uninstall the program that Updates the less often
I don't run either of those programs I rely on Avast! which updates daily (and is Freeware) and is very stable
For Nasties of the Ad variety I use Spywareblaster (updates roughly once per month)
and Main Firewall I have chosen COMODO which has an antivirus Program built in. This is the only configuration that is stable
NOTE This too is Freeware.Does react badly with certain other Firewalls in situ .I had a lock up when I first tried it with McAfee Personal Firewall still in place
