Help regarding Paypal sandbox use.

Can somebody assist me with the sandbox account testing.
I am trying to test my shop at http://www.techux.com
I have managed to integrate the shipping calculators from USPS,

but on the third step of checkout, it reverts back to previous page, instead of showing thank you or something.

–>In the sandbox account, The test-e-mail shows “Verify your account, .. .. “”

I was assuming it to be much simple task, as all of it is handled by wp-ecommerce plugin.

I seriously would appreciate any help on this. I am getting to nowhere since last week. Have read tons of articles, and help docs for this but with no luck.

thanks. 🙂