If spawning this dupe crashes your game then i got you.

Right click on garry's mod and go to properties. Then go to betas and click on the option that says: "x82-64 - Chromium + 64-bit binaries". Once you have done that update gmod and launch the game. When you do you will be presented with three launch options, click on the one that says: "32-bit" and the dupe should work.

If 32-bit doesn't work then try 64-bit. If it still doesn't work then it might be a problem with one of the addons you have installed.