Hi - getting constant errors after customers pay for their item. It used to be random but now is happening all of the time. I updated the software and it didn't resolve the issue.

Basically, after a customer pays (processor is PayPal), the page reloads and spits out "The page cannot be displayed because an internal server error has occurred."

An email from PayPal is received that they paid.
The transaction is marked unauthorized in the Admin portion of the site.

Any clue where to start digging?