Custom Crop Mark - .mrk file InDesign CC 2018,2019 dosn't work
Custom Crop Marks - I used CS3, CS6, CC 2017 and my file with custom crop marks was worked. Now in CC 2018 and CC 2019 isn't. I see PAGEMARKS DEFINITION FILE ERROR
I ran into this also. I found some people fixed it by removing all comments. It didn't work for me but it may work for you.