Error Code During Checkout on only one product

Still fighting with this error code.

"There was a problem finalizing your purchase. (TESTMODE) Line item 1 is invalid. Please go back and try again."

It only works on one product and all the other products go thru with no problems.
Try it for your self

http://www.platinumcarwash.com/store/services/1-full-detail-plus-2-platinum-car-washes/

The error comes up after I have confirmed everything on the confirmation page.
HELP? Thanks