Black render result in larger screen resolutions

[Duael]

Hello,
New user here.

When I attempt to use the higher predefined image pixel resolution settings for renders (anything above 4000 approx) I get a Black screen result in the render window. If I select a lower predefined setting, I will see my render result. If I then attempt to enter my own image resolution values, I get the same results. Black screen above 4k, visible image below 4k.

Any helpful suggestions would be appreciated.
Thank you

iMac, core i7, OSX 10.8.5, ZBrush Bridge. Keyshot 6.3.23