During my implementation of the Authorize.Net, I face some error and on checking its resolution, I found below links which may be helpful for you to work with it.
(1) Testing Guide
(2) Error 13: The merchant login ID or password is invalid or the account is inactive.
(3) Error 14: The Referrer or Relay Response URL is invalid.
(4) How do I add or delete Relay or Response URLs?
(5) Error: This transaction cannot be accepted (Authorize.net)
(6) Error: (103) This transaction cannot be accepted - Authorize.Net
(7) Authorize.net – User authentication failed due to invalid authentication values
(8) Auth Code 000000
(1) Testing Guide
(2) Error 13: The merchant login ID or password is invalid or the account is inactive.
(3) Error 14: The Referrer or Relay Response URL is invalid.
(4) How do I add or delete Relay or Response URLs?
(5) Error: This transaction cannot be accepted (Authorize.net)
(6) Error: (103) This transaction cannot be accepted - Authorize.Net
(7) Authorize.net – User authentication failed due to invalid authentication values
(8) Auth Code 000000