Marketplace Authorize.net Not Working

I am using a client supplied Authorize.net emulator (Plugnplay.com) in Marketplace and the transactions are kicking back the error..."There was a problem finalizing your purchase. Please go back and try again"
on the website.

However, in viewing our logs, the transition went through successfully and we returned a 'success' response to the shopping cart.

Everything on the Plug n Pay end seems to be working correctly.

So the problem seems to be with the shopping cart not properly handling the
success response. Unfortunately I didn't see anything in the settings that
would affect that.

Any ideas? Could we bypass the errors?