running winxp sp3 Avast free. Had the auto update and my pop mail stopped working (Thunderbird 3). Error message indicated a password problem. Used the unistaller and uninstalled (Safe mode) Used CCleaner to remove traces in registry and downloaded 5 and reinstalled that. Same problem. I repeated the uninstall reinstall process but still no luck. Uninstalled again and went back to 4.8 and all is well again.
Oddly, and maybe this can help the dev team, the problem was only with one pop account. It was the Bellnet.ca account Bell (Canada) Business high speed. Pop accounts with Telus and Network solutions worked fine.