I am using ZenCart 1.3.8a and I have looked everywhere for an answer to my problem. For some reason I cannot use the USPS shipping module. I have it all set up with USPS and I am in Production Mode (I even verified this), but I keep getting this error message:

We are unable to find a USPS shipping quote suitable for your mailing address and the shipping methods we typically use.
If you prefer to use USPS as your shipping method, please contact us for assistance.
(Please check that your Zip Code is entered correctly.)
I set it to debug mode and I get emails with the following:

<?xml version="1.0"?>
<Error><Number>-2147219085</Number><Source>Rate_Respond.DomesticRatesV2;SOLServerRates.Rate_Respond</Source><Description>Invalid XML Element cannot be empty according to the DTD/Schema.
</Description><HelpFile></HelpFile><HelpContext>1000440</HelpContext></Error>
Now as I am typing this I just got another debug email that says something different than the 10 or so I got before:

<Error>
<Number>80040b1a</Number>
<Description>Authorization failure. You are not authorized to connect to this server.</Description>
<Source>UspsCom:oAuth</Source>
</Error>
I get this message after I verified with USPS that I am on the Production Server. So I have no idea what is going on now.