I have done a lot of Googling online about this in the last few days.
I have determined the recent 15.05.2008 definitions file is corrupt.
If you'd like to download the last known good previous working "defs.ref" file (3.22MB) (13.05.2008), it is available on my Windows 95 FTP, also posted below in my signature. Download and save to your Lavasoft folder, usually C:\Program Files\Lavasoft\Ad-Aware SE Personal. When the download asks if you would like to replace the existing defs.ref file, click YES. This will restore your Ad-Aware to the last known funtioning definitions file.
Ad-Aware is not going to be supported forever; it is for this reason that I have made a point of saving the old definitions on my FTP. I try every update before rushing to upload the newest file. Who knows? Is it the end of the line for Ad-Aware SE?