[Plugin: WP e-commerce] Google Checkout Errors

I’m getting some errors integrating my Google Checkout with my Ecommerce plugin. When I click the buy-now button, it gives a “No+seller+found+with+id” error. I’ve verified my Merchant Id & Key are correct. I’ve uninstalled and reinstalled the plugin. I’ve tested it with different items as well. I’ve tried it in sandbox mode with a Google Checkout Sandbox account and it DOES work, but still not in Production mode. I’ve made sure to uncheck the “Shopping cart post security” box in Google Checkout settings (For extra security, my company will only post digitally signed XML shopping carts. (Google should reject all others)). I left the “API callback URL” field blank. I’ve also noticed when I click the Buy Now button I can see my FF browser trying to connect to sandbox.google.com/…

Any suggestions? I haven’t integrated a WP cart before, I’m all dry for options. ^^