Hello, I have two questions for you about the problem that you are experiencing. 1) Did this problem recently start happening? 2) Have you recently upgraded your Mac OS ? I should also point out that IDL 7.1 is no longer a supported version of because it is so old. In addition to that, when IDL 7.1 was released the supported version of the Mac OSX was 10.5.1. The version difference for the OS may be contributing to your problem. Also, if you are considering upgrading to Mac 10.10 it should be noted that I do not know of anyone who has successfully installed IDL 7.x on 10.10. You may want to try uninstalling then re-installing X11 and see if that fixes your problem.