I have the exact same problem: after downloading Chaser via GOG Galaxy 1.1, and clicking "Play" in the GOG Galaxy user interface, Chaser immediately pops up a dialog box that insists on my entering a CD key. I took the advice mentioned in this forum and changed the Chaser executable so that it would always run with administrator rights -- but that hasn't solved the problem. I'm still getting the dialog box that asks for the CD key even though Chaser is configured to run on my system (Windows 10) with administrator rights. So... I've sent an email to GOG tech support asking them for a fix or workaround. When I get back their reply, I'll post it here.