A number of people have reported crashes when pressing save or preview in r64. Woops. Let's get to the bottom of this as quickly as possible.
I have a feeling it might be specific to the 64-bit build. Is anyone having these issues in the 32-bit build of Construct 2?
Also, if you're having problems with this and you're using 64-bit Construct 2, does switching to the 32-bit build make it any better?
Edit: I think I've identified a possible issue and done a quick fix. Here's a beta of r65 (note: this isn't the real r65 release). If you've been having problems please install that and let me know if it works better!