I've realised on both mac's the crashes are very intermittent, some days it will crash 4 or 5 times, others it doesn't crash at all?
To get the clips to render in the work area I had to remove the warp stabiliser effect, which I shouldn't have to do as I have plenty of memory/Ram on my imac to run any effects, and keep all the files on an external hard drive (which again has never affected performance before and i've had after effects, photoshop, adobe and premier open in the past all at the same time)
However saying this I have had the same issues with rendering in the time line in after effects recently too and just gave up
Just really frustrating.