First Class International shipping options are screwed since USPS made a change to the web tools on Jan 4, 2010.
So far all I have found is this post on the Magento forum:
[url]Home - Magento Forums
And this post from 2 days ago on the same forum with a fix for Magento
[url]Home - Magento Forums
I never received a heads up on this from USPS.
I can’t find the USPS XML in my CS-Cart installation anywhere. The USPS.php script was no help.
Anyone have a fix for this?
I rely on this class of service for an inexpensive shipping option to overseas from the US.
I’m still using ver 1.3.5 - live and in production makes it harder to upgrade to 2.0…
Subject: 2010 USPS International Web Tools change
I appear to have solved this problem myself.
The shipping services are stored in the database in a table named cscart_shipping_services.
You need to edit the usps-code field for these services:
First Class Mail International Large Envelope
First Class Mail International Package
First Class Mail International Letters
Express Mail International (EMS)
Change them to:
First-Class Mail International Large Envelope
First-Class Mail International Package
First-Class Mail International Letters
Express Mail International
As you can see, USPS now wants the words First Class to be hypenated and they have removed the (EMS) from the Express name. These values are passed directly to USPS and need to be exact for the service to return a value.
It appears as though all other International Services are no longer used so you may have to update the services you have made available in the Shipping Methods forms in your admin. (example: First Class International parcels and flats no longer seem to be supported.)
Magpie you are a life saver. 
Just now I seem to only have EXPRESS SHIPPING on my checkout … I made the above changes earlier this week. I didn’t touch Priority Mail… so what gives? Anyone having problems right now? Is it USPS server or CS-CART?
James
http://www.rpgshop.com