SMS Gateway DATA command

I am trying to send a binary file (currently a small image) through our SMPP bind to a mobile phone through the CF SMS event gateway and I'm apparently missing something.

When i setup the structure and pass it off to the sendGatewayMessage function i get an error in my logs that says:

MSGateway (SMPPGateway) error while processing 'data' command:  java.lang.ClassCastException: org.smpp.pdu.GenericNack cannot be cast to  org.smpp.pdu.DataSMResp

The code I'm using is:

<cfscript>
    data = structNew();
        data.sourceAddress = [source];
        data.sourceton = 3;
        data.destAddress = [destination];

        data.messagePayload = binMsg;
        data.command = "data";
       
        z = sendGatewayMessage('SMPPGateway',data);
</cfscript>

the source and dest addresses are both valid and i can send regular SMS just fine.

I suspect I am missing an arg in the data structure but I can't seem to find anything in the docs about it so I'm not sure.  Any suggestions?

Thanks in advance.