In a classroom we installed GIMP (by dragging the executable into the Applications folder) on a bunch of Macs. We installed X11 too. GIMP worked on all Macs for a while, but now one Mac (and just one Mac) can no longer launch GIMP. Perhaps a student did something "funny" on this Mac, but I can't find evidence of that. Students do not have admin privileges. When you double-click it, it launches, appears for a split second in the menu bar and dock, and then immediately quits. There are no messages displayed. Restarting the Mac does not help. Repairing permissions does not help. Other applications can still be launched. The problem happens no matter who you log in as, either as a student or as an administrator. My next thought was to delete its preference and/or application support files, but I can't find any preference or application support files for GIMP. Just in case, I trashed X11 and GIMP and reinstalled them. The problem remained. What might be wrong? How might I gather more clues?