1) Verify if the webservice is running at the specified port?
2) Verify if the webservice has to undergo form based authentication, basic authentication, etc
3) Check if the firewalls are not causing any issue (In your case i believe this is not a problem, but still check it out)
4) Are you the only one consuming this service? Any other app is using it? If so find out what they are doing?
OMElement payload = <Create your payload>;