Hello. I'm experiencing the same symptoms as others using Ad-Aware 2008. Updates using both the program's Update button as well as the Start Menu Software Update button fail. Here's what I've tried to do to remedy the problem (but please note, all my efforts have failed).
I was using Version 220.127.116.11. I tried all suggested fixes including downloading current defs (core.aawdef) manually, without success.
I then uninstalled 18.104.22.168 and ran CCleaner (to repair registry errors which may not have been removed during uninstall), then reinstalled an earlier version (22.214.171.124). Updates still failed (couldn't update either the program version or defs).
I then uninstalled 126.96.36.199 and ran CCleaner again, then reinstalled 188.8.131.52 (which I had saved on a USB memory key). Updates still failed (couldn't update either the program version or defs).
Finally, after reinstalling 184.108.40.206, I again pasted core.aawdef to my C:\Documents and Settings\All Users\Application Data\Lavasoft\Ad-Aware directory. Tried one final update using both methods--still failed. "Arrgghhhh!"
This is acting more like a server issue than a program issue. You would think ONE of the versions I installed should have worked. There must be something preventing the programs from communicating with Lavasoft's server. There doesn't appear to be an issue with my Norton Internet Security Program Control settings--all Lavasoft programs are on Auto and can pass through the firewall. I'm running Windows XP SP3. Thanks in advance to Lavasoft for working on this problem!