Same here. There must be a problem with the site. You could try downloading the definitions file click here, and then replace the file defs.ref in the folder C:\Program Files\Lavasoft\Ad-Aware SE Personal.
I installed the new Ad-Aware version 126.96.36.199 a short while ago. Tonight couldn't get it to open or run, got message... 'System error fault 19811,cannot read graphics Application terminates' I then went on their web site was having no joy there, so uninstalled it, then reinstalled it again from from C-Net downloads, Registered it then updated and it is actually now doing a full scan at this minute.
Did I see somewhere the fault is caused by not registering the new version in the first place, I'm almost certain I didn't do it at the time. But done it now and all seems OK.