Yes, for Marlin firmware, you should only be using the Marlin20. This g-code is obviously for GRBL and will have issues running on Marlin firmware. Note that Don Gamble has taken the Marlin20 post processor (written by Guffy), and improved it. See this topic for the latest version. If you are having trouble running a laser from the Marlin20 post processor (or the Don Gamble version), post back to the forum with the particulars.