Ubercart Issue

Hi All

I am having problems with an Ubercart site whereby the cart gets cleared when the Checkout button is clicked. I can't for the life of me, replicate the problem. It happened to a customer using Chrome and Debian Linux. If anybody has this setup and you don't mind helping me test, let me know and I'll send through the website link. I just need you to go to the site put a few products in your cart, then try and checkout. I'm trying to determine if it's a procedural error or a browser/OS error.

Thanks Heather