I have a Developer Edition account as I am trying to do a POC on integration of SFDC using Tibco BW.
I have created a Workflow Rule which triggers an Outbound Message. The message will be recieved by a Tibco BW Web Service on tibco's end over HTTP.

Even though the URL in the outbound Message matches the Webservice URL, the outbound message get's stuck on the SFDC side with a Delivery Failure Reason '(403) Forbidden'.

Please tell me what is the reason for the error as there is no information that i could find on this. Also, how can i fix this.