Image in Tomcat

[gerito]

Hello. I´ve got two machines:
Machine A - Red Hat 7.2 and Tomcat 4.0.3 (server)
Machine B - Red Hat 7.3 and Tomcat 4.1.6 (client)

Now i´ve got an application (written in Java) that creates thumbnails from an Image object but this application doesn't run in machine A and it runs in machine B. The error starts when I use a method of AWT or SWING like someone of Image Class and this error is:

"java.lang.InternalError: Can't connect to X11 window server using ':0.0'
as the value of the DISPLAY variable"

X server in A machine is 'active'.

Thanks and greetings.