Stuck on Delivery Information page during checkout

[meburke]

I have an active store (but as of yet just a few sales), and I just received an email from a prospective customer stating that they could not checkout because it kept looping them back to the Delivery Information page. The last change I had made to my store was deleting countries in the database and adding back in United States as the only country available. This was originally done when I first set up the store and I had no problems, and I inadvertently did it again when I was trying to perform the same action on another store. I was logged into the wrong store (I know, I know)... I found a few other references to this problem in a Google search, and it seems like I've done everything that was suggested (such as recreating the customer account, checking the shipping and payment modules, etc.), but I still can't get it to work. However, the brand new store that I also deleted countries from (after realizing I'd done it on the wrong store) is working fine in checkout. Any ideas or suggestions would be greatly appreciated....