Help needed integrating Authorize.net SIM with c# asp.net web app


I have been trying to implement Authorize.net SIM integration with C# asp.net webapp.
1) I downloaded API for SIM sample code and just used my credentials within the code they provided .
but i am getting an error. as below:
(87) Transactions of this market type cannot be processed on this system.
2) In that sample code we dont have a response back from authorize.net, I am trying to figure out the way to get a relay response so that the users are redirected back to the website after transaction is done.
Please let me know, if any one has link to SIM implemented code with vb or C#.
thanks!! in advance