Seeing there hasn't been a difinitive answer yet, I'm hoping maybe a solution just hasn't been posted. I am having problems with the "Whoops!" message as well. Here's when I saw it (more data for ya)...

- using paypal express checkout
- choose to pay with credit card without logging into paypal (as if I didn't have a paypal account).
- upon completing the paypal transaction I am sent back to my site (good) but then receive the "Whoops!" message.

as of the time of this writing, I am using the absolute most up-to-date version of zen cart.. i just installed it today. all other facets of payment are working correctly as far as i can tell.

an additional interesting thing... if, when i'm making the purchase, i click on the paypal button - i go to paypal, do my thing there, go back to my site and have to continue through 2 more pages to complete my order. If when I making the purchase I click on the zen cart "continue to checkout" instead of the paypal button, and then i go to complete my order through paypal, when the transaction is complete i immediately go to the final confirmation page with the download link etc.


any insight on any of this would be greatly appreciated it!