OSX Mountain Lion (10.8) seems to change the order of the MAC addresses presented to flexlm licence processes. There is a page about various problems at the Mathworks website:
Why am I unable to launch MATLAB after upgrading to Mountain Lion?
At the bottom of the page it gives the command to run to determine which address the licence process is seeing:
/Applications/MATLAB_.app/etc/maci64/lmutil lmhostid
