I'm testing the cart with my shop http://www.continental-crumbs.com
1. Problem:
When I press submit from the chart to go to sandbox.paypal.com mostly nothing happens! Goes back to main shop page!
2. Problem
When I was able to submit and came to sandbox the backlink produces this output:

As you can see the page is produced twice. The upper part shows error, the lower part shows the right reply.
3. Problem:
I cannot get rid of the "download not allowed message"
Many Thanks,
Oliver