I just found this on the Lavasoft forum:

"The appearance of hanging usually occurs when 'Scan archives' is selected. Its not actually stopped scanning however. What's happening is Ad-aware is de-compressing/ unzipping files to check the contents for suspicious files, the Ad-aware re-compresses the files. This can take some time.
If this is the setting that's effecting your scans,
Try this
Open your Ad-aware,
Click the "Settings" (The Gear) button at the top right to display the "Settings" main menu.
Click "Scanning".
Un-Tick 'Scan within archives',
Click 'Proceed'.
Also try shutting as many programs/process as possible. (I.E firewall Anti-Virus etc.) Please make sure that you
Unplug/disconnect your Modem before disabling your Anti-Virus/Firewall
Just remember to turn them back on"