Error that transaction was approved

When someone completes the form, the transaction goes through, but this error is displayed:

An error occurred while trying to report this transaction to the merchant. An e-mail has been sent to the merchant informing them of the error. The following is the result of the attempt to charge your credit card.

This transaction has been approved.
It is advisable for you to contact the merchant to verify that you will receive the product or service.

How can I fix this or at least hide the error from the user?