Crashing Error on RunRev 2.7.4.291

[Dave]

Hi,

I have a stack file that crashes RunRev  2.7.4.291 every time I try  
to open it. It's the same Stack File that I am trying to get to  
access the External Command as per my posting "Externals Under  
2.7.x". Any ideas on how to make this work again?

Some related questions:

1.  Is 2.7.4.291 worth using? I am running on a Mac only at present.  
I've had no end of problems using versions prior to 2.7.4.291, but I  
was told (perhaps incorrectly) that 2.7.4.291 was "a lot better". Now  
I'm not so sure.

2.  I am trying to make it Access an External Command on Intel Mac's  
only. Is this feasible under 2.7.4.291?

3.  Can I access an Mac/Intel External Command using version 2.6.6.152?

Thanks in Advance
All the Best
Dave