Symptom:
The error looks something like this:
Warning: opendir(/payment/) [function.opendir]: failed to open dir: No such
file or directory in /home/pixelorg/public_html/payment/payment_manager.php
on line 12
Problem:
Your 'Server Path to Admin' is not set in the 'Main Config'.
Solution:
Go to Main Config, set the 'server path to admin' to the recommended settings.