2Checkout error PE103 - help!

When users try to checkout using my form I'm getting the following error message from 2Checkout:

An error has occurred during checkout.
Please contact the seller and reference the error code below.
ERROR CODE:PE103

This is what their KB says: help.2checkout.com/articles/Knowledge_Article/Error-Code-PE103/

Can someone help me with this? It's really screwing up an upcoming event for which we're trying to collect registrations, and I'm not getting any answers to my help tickets.

This is the form: www.gonggongcommunications.com/component...form_id,2/view,form/

I can PM login details upon request.

THANK YOU!!!!!!!!!!!