Error with user authentication

I have a web service and it is deployed on two machines- a PC and a UNIX machine. Both of these machines have the Resin server installed on them. My web service is supposed to call a backend RPG program that authenticates the user specified in the incoming XML message. When the web service on the PC calls that backend RPG program, it is successful. When the web service on the UNIX machine calls the backend RPG program, it gets an error saying that the backend RPG program cannot be accessed. The same web service is installed on both machines. Do any of you have any idea why the web service on the UNIX machine gets that error, but not the web service on the PC? Do you think that there might be something wrong with the Resin server configuration on the UNIX machine?