I never thought that even DISPLAY will going to give me tough time. Our client doesn't allow us to use VNC due to security reason. So we do not have any other option other than Xvfb at server End. We did start it and as expected xclock worked and no output. So I tried testing PDF output of my Active User conc program, it failed due to lack of Windoes Manager running at server. So I have to start twm at server end give xhost +. Vola it worked !!! Now another issue which I can forsee for my production as we were using Virtual host, to avoid any confusion in production cutover I used DISPLAY=`uname -n`:1.0
Happy Troubleshooting !!!