The strange thing is that you shouldn't need to run the script at all. What it does is set up permission on a directory used for locking, but the version of RXTX included with Arduino shouldn't use locks at all (since they're in a non-standard location for the Mac, they don't really help anyway, since most other programs don't know about them). Do you have any versions of librxtxSerial.jnilib or comm.jar or jcl.jar in any of your Java directories?