USPS Error Message

I am trying to check out of my shop (http://onlineshop.yarniapdx.com), and at Step 4, when I am given the shipping options, both UPS real-time shipping options as well as In-Store Pickup show up fine; however, under the United States Postal Service heading, there is the following error message:

"RECTANGULAR is an invalid container type for a REGULAR package and ALL service."

In the past (before I upgraded) I was using USPS real-time shipping quotes -- it seems like there is some hiccup in there now after upgrading, how can I fix this?

Thanks,
-lindsey

Post office backend calls seems to be pretty stable for me. Look over something in your settings. Like if you set the LXWXH correctly.