Invalid ARB payment notification received.

All of my ARB silent posts are coming through as invalid. Looking at the dblog I see a silent post come through, and it appears to be formatted correctly.

Example below, some values sanitized. The order is the correct number, and the customer info matches up.

ARB Silent POST received for order 2648:
Array
(
    [x_response_code] => 1
    [x_response_reason_code] => 1
    [x_response_reason_text] => This transaction has been approved.
    [x_avs_code] => Y
    [x_auth_code] => 02013P
    [x_trans_id] => XXXXXXX
    [x_method] => CC
    [x_card_type] => MasterCard
    [x_account_number] => XXXXXX
    [x_first_name] => FNAME
    [x_last_name] => LNAME
    [x_company] => 
    [x_address] => XXX Some Lane
    [x_city] => CITY
    [x_state] => ST
    [x_zip] => 00000
    [x_country] => US
    [x_phone] => 
    [x_fax] => 
    [x_email] => name@email.com
    [x_invoice_num] => 2648
    [x_description] => Order 2648 -
    [x_type] => auth_capture
    [x_cust_id] => 346
    [x_ship_to_first_name] => 
    [x_ship_to_last_name] => 
    [x_ship_to_company] => 
    [x_ship_to_address] => 
    [x_ship_to_city] => 
    [x_ship_to_state] => 
    [x_ship_to_zip] => 
    [x_ship_to_country] => 
    [x_amount] => 29.99
    [x_tax] => 0.00
    [x_duty] => 0.00
    [x_freight] => 0.00
    [x_tax_exempt] => FALSE
    [x_po_num] => 
    [x_MD5_Hash] => THISWASALEGITHASH
    [x_cvv2_resp_code] => 
    [x_cavv_response] => 
    [x_test_request] => false
    [x_subscription_id] => 33939392
    [x_subscription_paynum] => 1
)

But every time the next message in the log is "Invalid ARB payment notification received."

If I look at the "admin/store/orders/recurring" page, I see orders that have the next billing date in the past.
The card does get charged, but something is preventing the module from updating the order. Since the order doesn't get updated, the purchased roles don't get reapplied.

Any advice you can give me would be greatly appreciated.

Ubercart 7.x-3.0