Failure: The XML document is not well formed

This error can be returned by the UPS Rate servers if an invalid address element is received.  This error usually means that the address information your provided is incorrect, or does not meet UPS requirements.

Be sure you have entered a valid and complete default address in the UPS setup page, "UPS Rates" in PDAdmin.  If you are testing the Add-On during checkout or in PDAdmin, you must use valid addresses.

Also verify all other default UPS Add-On settings in PDAdmin.