I believe I have discovered a possible conflict between ZA Free Firewall + AV and Spybot 2.1.

After installing Spybot 2.1, the AV update in ZA no longer completes. It stops at 2% and returns the helpful error message "ERROR." Then, the update to the software itself tries to run, but, doesn't appear to do anything. I have to cancel and then cancel again to get the updater to stop and exit.

I tried disabling Spybot's Live Protection, but, that didn't help. When Spybot was uninstalled, the checks for updates complete properly in ZA. So, I installed Spybot again, and the problem returned. Uninstalling Spybot again resumed proper updating.