This file did not exist in the new installation. I cannot remember if flatone.php is part of a module, but unless there was a old database reference, why would a new installation have the need for a file that does not exist in the original files?

Anyways, I added the file from my backup and PayPal express went straight through. No more white page. I think that the second time I imported everything, it seemed to 'take' better. Thank you for the help.