Authorize.Net Error E00003 - Data at the root level is invalid

[davi7852@yahoo.com]

I am trying to process payments on my website, but am getting an error when submitting payment.  It gives me the:
Warning: Unrecognized response from AuthorizeNet: ErrorE00003Data at the root level is invalid. Line 1, position 1

All my research points to an XML or JSON issues, but I can't find where that file originates.  Any help would be appreciated.  Here is my site:
http://hotmeltadhesiveequipment.com/

Please try to submit a payment for any product and you will see the error code pop up.  I have searched my files for "createTransactionRequest" but can't find anything.

Thanks!

Ryan