perimeter error with 2CheckOut

[CAguy]

I did a new install this morning of the zen cart 1.3.9
Added the 2checkout module
set up the information as needed.
Placed one item in the store to make a purchase.
Placed the item in the cart, went through checkout
all the way to the end but when it gets sent to 2checkout.com,
I get a parameter error:

Parameter Error
A pparameter error was encountered when attempting to process this sale. Please notify the supplier so that this can be resolved as soon as possible.

Anybody have any ideas as to why I get this error?

I spent an hour on the phone with tech support at 2co and he has never seen this. He had me check some of the php files and settings and said it is set up correctly.