I've had the same freezing problems on my PC, using deep scans, with Ad-Aware 2008 and also A-Squared. I also have Zone Alarm firewall installed.
However, I have the same versions of the same programs on my laptop, and there is no problem.
After many investigations and experiments I found a cure which works here.
Unistall Ad-Aware 2008, and also uninstall Zone Alarm.
Re-install Ad-Aware, and THEN re-install Zone Alarm - IN THAT ORDER....
Deep scan issues with anti-virus and anti-spyware seems to be cured by installing Zone Aarm as the last program in your security suite.
(It sorted out the deep scan issues with A-Squared too...)
