How to get more verbose runtime error logs

I’m getting the following error in my player.log file on development OSX standalone build (PC build works fine):

Receiving unhandled NULL exception
Obtained 15 stack frames.

Nothing else, no stack trace, no library list, nothing. Those 2 lines are the complete last two lines of the log (and the program hangs). The build is already a development build and the Mac Console shows no errors. I tried adding log statement to see where it is occurring, but with no success, it seems to move around! It also happens only about 50% of the time.

Is there some why of getting more information out of the program so I can see what, or where, the error is?

It turns out this is due to interaction between the Steam Overlay and Unity3D. I have yet to see a way to fix it other than turning of the Overlay.