I have a Web service deployed on two different UNIX servers. Both of these UNIX servers have the same Java application and the same keystore file. When I send an XML message from my PC to Java application on one of the UNIX servers, I get a successful response. However, when I send the same XML message to the other UNIX server, I get an error message that says that the X11 DISPLAY variable was not set. I have the DISPLAY variable set on both UNIX servers and I also have the DISPLAY variable set on my PC. Why do I get the error on one UNIX server, but not on the other?