I'm having a similar problem, although I'm having an issue with the file that Ad-Aware SE (mine isn't pro) is actually downloading (cannot be read, or something). For now, if it works, you could download the latest defs in a zip file, here:
http://download.lavasoft.de.edgesuite.net/public/defs.zipThe full instructions from Lavasoft:
Close Ad-Aware.
Download the latest definition file in a ZIP format and save the file to a temporary location.
Unzip the contents of the file either with your favorite ZIP utility or the built-in support in Windows to the Ad-Aware installation directory, which usually is C:\Program Files\Lavasoft\Ad-aware SE\.
Open Ad-aware.
Confirm that the latest definition file is installed by checking out the Initialization Status in the main program window.This worked for me.

Spidey