Hi Samccb,
Ahh I was not aware that this issue was on mac. I attempted to repro on the macbook pro internally, but was not able to do so. It seems that we are going to need some more information to get to the bottom of this issue. If you could, would you go to this address:
and follow the instructions that are listed under the sections titled:
The Launcher fails to load, or crashes on load
None of the Above Helped - Getting Debug Logs
These sections provide detailed instructions on how to get the verbose log, and Dxdiag files that will be needed to submit a proper bug report. Once you have these files, just zip them up using the utility of your choice, and attach them to a comment. Once I have all of that information I can put together a bug report for you and submit it to the developers.
Thanks for your patience while we get this worked out,