I had this same problem when trying to run Sage. My problem arose because the standard OS X python is being called instead of Sage's python, because the install script puts the path to Sage's executables AFTER /usr/bin/ in the $PATH variable. My work-around was to open a new terminal window and enter the following two lines: export PATH=/Applications/Sage-4.7.2-OSX-64bit-10.6.app/Contents/Resources/:$PATH