Well, I did talk to the Authorize.net help line (chat, actually), but in the process also discovered the log files for the return authorization. I hadn't realized before that they were separate files.

So after looking at those, it seems the transaction in going through fine, but is failing when it comes to verifying the hash. Here is a copy of the return log:

Feb-11-2008 10:16:48
=================================

Response Code: 1.
Response Text: (TESTMODE) This transaction has been approved.

Results Received back from Authorizenet: Array
(
[x_response_code] => 1
[x_response_subcode] => 1
[x_response_reason_code] => 1
[x_response_reason_text] => (TESTMODE) This transaction has been approved.
[x_auth_code] => 000000
[x_avs_code] => P
[x_trans_id] => 0
[x_invoice_num] =>
[x_description] => Website Purchase from TriathlonDVD.com
[x_amount] => 64.95
[x_method] => CC
[x_type] => auth_only
[x_cust_id] => 2
[x_first_name] => David
[x_last_name] => Perry
[x_company] =>
[x_address] => 101 Main St.
[x_city] => Franklin
[x_state] => Tennessee
[x_zip] => 37064
[x_country] => United States
[x_phone] => 615-330-8718
[x_fax] =>
[x_email] => [email protected]
[x_ship_to_first_name] => David
[x_ship_to_last_name] => Perry
[x_ship_to_company] =>
[x_ship_to_address] => 101 Main St.
[x_ship_to_city] => Franklin
[x_ship_to_state] => Tennessee
[x_ship_to_zip] => 37064
[x_ship_to_country] => United States
[x_tax] => 0.0000
[x_duty] => 0.0000
[x_freight] => 0.0000
[x_tax_exempt] => FALSE
[x_po_num] =>
[x_MD5_Hash] => 12C09A79F1B0F818A9A4BF073C1A8886
[x_cavv_response] =>
[x_test_request] => true
[x_relay_form] => TRUE
[zenid] => 5923380061bcf5e36c57a7fbfc588424
[HashValidationValue] => 1817F8884A26A007598ACE1FE1332939
[HashMatchStatus] => FAIL
[url] => https://secure.authorize.net/gateway/transact.dll
)


To double-check that the hash values were correct, I re-saved the one from the zencart admin over to the authorize.net admin. So they're definitely the same, just not sure why that last bit is failing.

Thoughts? Thanks in advance for any help.

David