I have the same WP installation with WP eCommerce plugin in stalled on two hosting servers, one with GoDaddy and one with Arvixe. The plugin includes a UPS shipping module and I have set this up exactly the same on both servers. In Godaddy the UPS shipping module pulls and display rates accordingly, but on Arvixe it does not. I am not sure if it is an AJAX issue or what, but Arvixe's server has a setting that is not setup correctly as far as I can tell. I have also tested the plugin shipping module on Hostable.me and it works correctly, so I have conclude that it is an Arvixe issue.

Here is a link to the Arvixe products page: http://www.bellinghamdining.com/products-page
1) Add product to cart
2) rollover "Products Page" menu item > select "Checkout"
3) Enter "Shipping State" and "Zip" > click calculate

You can see the page does a post back but the shipping quote does not display

Here is the link to GoDaddy, exact same set up and process above: http://test.k-elementsdesign.com/?page_id=4
The page posts back and displays rates from UPS with no errors.

Both are Windows servers.

Here is the plugin:
http://getshopped.org/
http://wordpress.org/plugins/wp-e-commerce/

Thanks for any insight