People have been reporting problems getting the latest def file to update, here's what I did to fix it when it happened to me.

To fix this glitch, I removed the file called defs.ref and the defs.ref backup file. It then put up a error message saying it could not find definitions when I restarted Ad-Aware, ignore it. Click on "Check for updates now" and it will then download the latest definition file...

Haven't come across the problem yet, but thanks for posting your fix, it could help people if they do run into that prob.