Charging people twice if they miss a field

I have a cart that, if someone misses a field and the red warning text comes up and tells them they missed something, and they've already put in their credit card info (authorize.net AIM), it charges them and then AGAIN when they resubmit.

The customer said:
"When I tried to checkout online to place this order the first time, your website gave me an error message. I corrected the red highlighted information and tried again. I was successful checking out the second time. I received the order and everything was correct/as ordered. However, my credit card was charged twice for $167.13. Please refuind the erroneous second charge of $167.13, and let me know when you have done so."

Authorize.net claims it's not their fault and that they didn't get any error message on the first transaction.

Is there anything that can be done on the cart side to stop this?

avansant:

Is there anything that can be done on the cart side to stop this?
Probably. You'll need to find out what the exact error was, since what you describe is not normal Zen Cart or AIM module behaviour.

Things that will help:

• turn on AIM module debug log-to-file
• consult the myDebug-xxxxx.log and AIM-*.log files in the /logs/ folder on your server, particularly after re-triggering the exact same scenario again.