Keyshot for Zbrush crash all the time

[jbmonge]

 Hello guys
I run a mac pro Software  OS X 10.9.5 (13F34) with 64 gig of memory-Processor  2 x 2.4 GHz Quad-Core Intel Xeon-Graphics  AMD Radeon HD 7950 3072 MB

I try to make a scene on keyshot for Zbrush but very very often when i try to change a material or just to enlarge a view of my mesh Keyshot Crashes. it will becomes impossible to finish a scene for me so i am really disappointed. i just work for the moment on a part of my scene which have several millions of polygones on ten subtools I used bump map and specular map often on my scene, and that crashe all the time. This situation is really frustrating. please if you have solution