Hi, apologies for that (and my very late reply (I've been away from the indie game dev scene for a bit over a year)). After importing my asset into a new project, I was able to get it working by removing "Room1" and setting "Rm_Level" as the starting room. I think the error happens if "Obj_VARMS_windows" or "Obj_VARMS" aren't in the starting room. It's been ages since I've worked on / used this but for your own game, I think just putting "Obj_VARMS_windows" or "Obj_VARMS" (if using full screen) in your starting room will work. Be sure to read through "README.txt" and code/comments (so you fully understand it all) and tweak it to your liking within your game :).
Also, I will update this soon to get rid of "Room1", dunno why it was included.