This is a new bug introduced with some recent version of Max 7 where rewire always crashes once the sequencer is begun in the Master application.
I spent a good few hours trying to get a working version of mlrv going with Max 7 in Yosemite and found it simply not possible with any soundcard other than the built-in audio driver. Brian and I are currently discussing the best approach to provide a working version compatible with the audio driver changes in OS X since 10.10.
Apologies for the delay, but this has turned into a much bigger discussion on how to provide legacy support in a rapidly changing software environment. Hopefully we’ll have something more to share in the near future.