I'm using godaddy as the host. I configured the cURL proxy in the admin. I also enabled SSL. I'm using Authorize.net (Sim).
I also have no idea what the difference is between Authorize.net SIM or AIM.
I am a n00b at this. Please help.

These are the two messages I get when the transaction fails:

Sent to Authorizenet: Array
(
[x_login] => *******
[x_amount] => 26.36
[x_version] => 3.1
[x_method] => CC
[x_type] => auth_capture
[x_cust_ID] => 2
[x_email_customer] => TRUE
[x_company] =>
[x_first_name] => xxxxxxxxxx
[x_last_name] => xxxxxxxxxx
[x_address] => xxxxxxxxxxxx
[x_city] => xxxxxxxxx
[x_state] => xxxxxxxx
[x_zip] => xxxxxxxxxx
[x_country] => xxxxxxxxxxxxxx
[x_phone] => xxxxxxxxxxx
[x_fax] =>
[x_email] => xxxxxxxxxxxxxxx
[x_ship_to_company] =>
[x_ship_to_first_name] => xxxxx
[x_ship_to_last_name] => xxxxx
[x_ship_to_address] => xxxxxxxxxxx
[x_ship_to_city] => xxxxxxx
[x_ship_to_state] => xxxxxxx
[x_ship_to_zip] => xxxxxx
[x_ship_to_country] => United States
[x_Customer_IP] => xxxxxxxxxxxxx
[x_relay_form] => TRUE
[x_relay_URL] =>
http://getyourwebstore.com/trumystic...eckout_process
[x_invoice_num] =>
[x_description] => Website Purchase from Trumystic Online Store
[x_duplicate_window] => 120
[x_fp_sequence] => 629
[x_fp_timestamp] => 1204818725
[x_fp_hash] => a78d983beef5cb90895dc899a2079371
[x_card_num] => XXXXXXXXXXXXXXXXXXX5121
[x_exp_date] => 0910
[x_card_code] => 584
[zenid] => 263l1ucs797f93as71fffq9pe1
[url] => https://secure.authorize.net/gateway/transact.dll
)

and this message too

Response Code: 3.
Response Text: This transaction cannot be accepted.

Results Received back from Authorizenet: Array
(
[x_response_code] => 3
[x_response_subcode] => 1
[x_response_reason_code] => 99
[x_response_reason_text] => This transaction cannot be accepted.
[x_auth_code] =>
[x_avs_code] => P
[x_trans_id] => 0
[x_invoice_num] =>
[x_description] =>
[x_amount] => 26.36
[x_method] => CC
[x_type] => auth_capture
[x_cust_id] =>
[x_first_name] =>
[x_last_name] =>
[x_company] =>
[x_address] =>
[x_city] =>
[x_state] =>
[x_zip] =>
[x_country] =>
[x_phone] =>
[x_fax] =>
[x_email] =>
[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_tax] => 0.0000
[x_duty] => 0.0000
[x_freight] => 0.0000
[x_tax_exempt] => FALSE
[x_po_num] =>
[x_MD5_Hash] => 27CE60D8ACBF315474AC69527725DD70
[x_cvv2_resp_code] =>
[x_cavv_response] =>
[x_test_request] => false
[x_relay_form] => TRUE
[zenid] => 263l1ucs797f93as71fffq9pe1
[HashValidationValue] => 27CE60D8ACBF315474AC69527725DD70
[HashMatchStatus] => PASS
[url] => https://secure.authorize.net/gateway/transact.dll
)