I dled it and when I click play i get this error

Runtime Error!

Program:...program files(x86)/GOG Galaxy/gamesNWN Diamon/nwmain.exe

Abnormal program termination.

any idea why this is happening?

It's installed in the wrong directory.

NWN must be installed and run directly off your main drive like C:\NeverwinterNights\NWN

Don't use the "play" button.

Make a shortcut directly to nwmain.exe and use that.

Make sure the shortcut has it's compatibility tab to include:

Run this program in compatibility for: Windows XP: SP3
Disable Display scaling
Run this program as administrator