Hey folks. I'm running nopCommerce 1.90 and ran into the same issues with USPS. We took a couple of steps:
1) Setup a Web Tools Kit with USPS at https://secure.shippingapis.com/registration/
2) Configure the USPS Shipping Rate Method. Make sure you copy and paste your username and password from the email. The URL that worked for me is http://production.shippingapis.com/ShippingAPI.dll.
3) Find line 59 in ~/Modules/EstimateShipping.ascx and update <%#Server.HtmlEncode(Eval("Name").ToString();%> to <%#Server.HtmlEncode(Eval("Name").ToString().Replace("<sup>&reg;</sup>",string.Empty)) %>
4) Find line 12 in ~/Modules/CheckoutShippingMethod.ascx and update <%#Server.HtmlEncode(Eval("Name").ToString();%> to <%#Server.HtmlEncode(Eval("Name").ToString().Replace("<sup>&reg;</sup>",string.Empty)); %>
Enjoy :)