On or about 19 Sept, Google made some changes to their Gmail service.
I had been using my Palm Treo 650 smartphone on the Sprint network to get my email on the go. These changes made the Versamail auto-sync stop working. I couldn't download new email manually either. I was still able to check my messages via webmail on the Blazer browser, but that was a pain in the butt.
I finally had a chance to research this issue, and came across a very helpful Google Groups topic. Basically, I had to disable POP completely, and then re-enable it for all new email. And voila...we're back in business!