Marketpress - Entering full state name causes errors

One of my MarketPress users reports:

People are still having problems with the checkout on our website. We finally figured out that there is a problem with the box where the costumers enter their state. If you type the name of the state, not the initials, an error message appears and the sale is stopped. We need to at least have something temporarily added that tells them to only use an abbreviation. We've been losing quite a few sales.

Can this be changed to a drop-down box with states to remove this issue?