Your site uses USERTRUST certificate with is not in the list of Google Checkout supported SSL certificates (check
http://checkout.google.com/support/sell/bin/answer.py?hl=en&answer=57856 for list of valid certificates)
Also and error you pointed reveals that your server throw an 501 server error in response to Google Request.
However when manually sending XML from Google Console you posted, result returned is:
<?xml version="1.0" encoding="UTF-8"?>
<merchant-calculation-results xmlns="http://checkout.google.com/schema/2">
<results>
<result address-id="670245329961552" shipping-name="UPS - Next Day Air">
<shipping-rate currency="USD">80.80</shipping-rate>
<shippable>true</shippable>
<total-tax currency="USD">0</total-tax>
</result>
<result address-id="670245329961552" shipping-name="UPS - Ground">
<shipping-rate currency="USD">11.56</shipping-rate>
<shippable>true</shippable>
<total-tax currency="USD">0</total-tax>
</result>
<result address-id="670245329961552" shipping-name="USPS - Priority Mail">
<shipping-rate currency="USD">0.00</shipping-rate>
<shippable>false</shippable>
<total-tax currency="USD">0</total-tax>
</result>
<result address-id="670245329961552" shipping-name="USPS - Parcel Post">
<shipping-rate currency="USD">0.00</shipping-rate>
<shippable>false</shippable>
<total-tax currency="USD">0</total-tax>
</result>
</results>
</merchant-calculation-results>
So the script itself works as intended, so I assume the problem is your certificate.