I'm not sure what the problem is here but there's a couple of things you can try.
1. Are you running the program as a different user to the one you logged on as? If so, you may need to set the DISPLAY variable for the new user (e.g. root) and allow access. In this case the procedure would be.
i) As your own user, open a terminal window and type xhost +
ii) su to the other account
iii) Type export DISPLAY=<hostname>:0
iv) Launch the app.
(Note xhost + is not good for security. Use it to check the issue, then read the xhost man page to find a better version of the command if it works).
2. If you are running as your own user then something is wrong, since launching apps should work. However, there's a good chance that using the method above - xhost + and export DISPLAY - will still work.