Check Door is GRBL telling you that the pin it uses to monitor the lid switch has been triggered (it thinks your laser lid is open). What version of GRBL are you running, and on what kind of machine?
There may be something in the wiring that isn’t grounded properly. AwesomeTech has guidance on their site for setting up a door switch, but they don’t mention anything about false triggers. I would check with them. https://awesome.tech/mini-gerbils-peripherals/
