[oXygen-user] prevent multiple instances on OS X

I've read a couple of postings here about adding the property -Dcom.oxygenxml.MultipleInstances=false to the Java command line in the oxygen launch sh script. I've added that property to my environment, but I'm still getting multiple instances when launching via the sh. Is there something different that must be done on OS X versus Linux (which is the OS discussed in the threads I've seen)? more details: oXygen 12, OS X 10.6.5, JRE 1.6.0_22 TIA, Bob