Mac OS X GC not registering mouse clicks

[Rich Harover]

Hello list from a newb.

GC is running fine for me on my MacBook Pro (Mac OS X 10.12.6).

I installed v 2.6.18 and tried to run on my iMac (Retina 5k, late 2015 
model running OS X 10.12.6), and while the program launches just fine, 
it won't register any mouse clicks of any kind.  In fact, I have to kill 
the program to quit.

Any thoughts or advice is appreciated.

Thanks,

R