I received the below email from Authorize.Net regarding the issue. It a nutshell, it looks like there was a timeout.
**Please DO NOT REPLY to this message. E-mail
[email protected] if you
have any questions.
Authorize.Net Merchant,
Your script timed out while we were trying to post transaction results to
it.
Transaction ID: 2458356050
Transaction Result: This transaction has been approved.
The following message was displayed to the customer:
------------------------------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.