Would you like to move aside the existing file and use the standard X11 environment?
[No] [Yes]

Got this error when loading up Gimp on Leopard, wouldn’t do anything, not even let me select No or Yes. How I fixed it was to delete the file /Users/[username]/.ixinitrc

Open a terminal and type:
rm ~/.xinitrc

Then quit out of X11, and restart whatever application you were trying to use when this happened