I just got a reply from Authorize.net, that the development test account delimiter is set to "|". I set the delimiter from "," to "|", and the messages the same.

Drupal message:
We were unable to process your credit card payment. Please verify your card details and try again. If the problem persists, contact us to complete your order.

Watchdog error:
Payment failed: Credit card payment failed: The transaction was unsuccessful.

Order comment:
Credit card declined: $0.00

Also, I'm getting this error on occasion, but it disappears if I try the order again:
"warning: split() [function.split]: REG_EMPTY in /home1/luluband/public_html/lulubandhas/dev/sites/all/modules/ubercart/contrib/uc_cim/uc_cim.module on line 444."

We've tested the developer account on eCommerce, and it works fine.

Any ideas?

Thanks,
Andrey.