404 response when calling external web service from amazon ec2

When I call an external web service from Amazon EC2 server I get a 404 response for the request. When I call the same web service locally开发者_运维百科 it works fine. Can anyone tell me why this happens?

It is entirely possible that the owner of the service has been seeing too much abuse from Amazon's IP range and that they have blocked access to the API from EC2. Normally however I would expect them to send back an Access Denied rather than a 404 Not Found.