Authorize.net Sends Response "1" but Zen Cart Throws Error

Hello!
I've been using Zen Cart for a while on an older installation (1.2.7) but just this week managed to upgrade to 1.3.8a. It took a while to do the upgrade, but everything was straight forward and worked well, until I did my first test transaction. I'm using the Authorize.net SIM module with all the correct settings (I have verified this with Authorize).

I'm in production mode on both sites and when I run a card (I've tried four cards, two active Visas and a Discover and an inactive Visa) I get the correct response from Authorize either accepted or declined (see logfile below for accepted card) but either way Zen Cart throws the "There has been an error processing your credit card. Please try again." error in response and the order is not saved.

I do notice that the Hash fails, but I have confirmed that I have the correct Hash in both Authorize and Zen Cart.

I hope that's enough information to diagnose the problem. Thanks!

Oct-15-2009 12:07:48
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Response Code: 1.
Response Text: 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] => This transaction has been approved.
    [x_auth_code] => 060713
    [x_avs_code] => Y
    [x_trans_id] => 2657055350
    [x_invoice_num] => 
    [x_description] => Website Purchase from Good Steward Books
    [x_amount] => 0.85
    [x_method] => CC
    [x_type] => auth_capture
    [x_cust_id] => 2333
    [x_first_name] => Daniel R.
    [x_last_name] => Ziegler
    [x_company] => 
    [x_address] => 9827 Rosedale-Milford Center Rd.
    [x_city] => Irwin
    [x_state] => Ohio
    [x_zip] => 43029
    [x_country] => United States
    [x_phone] => 740.604.1316
    [x_fax] => 
    [x_email] => drziegler######################
    [x_ship_to_first_name] => Daniel R.
    [x_ship_to_last_name] => Ziegler
    [x_ship_to_company] => 
    [x_ship_to_address] => 9827 Rosedale-Milford Center Rd.
    [x_ship_to_city] => Irwin
    [x_ship_to_state] => Ohio
    [x_ship_to_zip] => 43029
    [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] => E2AE1BDD4243E2994DBCB107FB7C1A98
    [x_cavv_response] => 
    [x_test_request] => false
    [x_relay_form] => TRUE
    [zenid] => 758fae8e7219ebcf25338e605b5f390a
    [HashValidationValue] => FD2651ADAAFD97EEBC29A52F78F7641D
    [HashMatchStatus] => FAIL
    [url] => https://secure.authorize.net/gateway/transact.dll
)

Whatever you use for a hash code must be less than 20 characters. I suggest choosing another shorter word/phrase for your md5-hash value.