Unable to create shipping label

Trying to make a label for a customer that I have already sent packages to in the past, using the USPS service. Suddenly I get a message telling me "You have entered a non-deliverable Delivery Address. Please verify address, including apartment, suite, etc." I'm wasting valuable time with this nonsense when I could be working on a million other things. I've spent an hour trying to get this to work and I'm just done. I know there's nothing wrong with this address. If there was, wouldn't I have been unable to print labels for them in the past? I'm assuming this is a temporary issue with the site, as opposed to some whacked out new policy or something.