it's really strange. the problem is that the SConstruct file tries to detect the path of the racket binary by executing 'which racket', which does not seem to work on your system. we should figure out why this happens.So; any ideas about next steps or tests would be welcome.
if worst comes to worst you can pass the racket path to scons using command line parameters like:
scons RacketPrefix=/Applications/Racket\ v5.1 best, gabor
