Error while testing message from Integration Engine.

Hi,

Trying to send message to Integration engine from RWB, using test mesage tab in Integration engine.

I pasted the payload(IDOC payload) , entered sender service, interface name and namespace and also username and password. Selected quality of servie as Exactly once.

While sending the message getting the following error - "Error while sending".

What could be possible reasons for this error.

Thanks.