This is a known issue with RPGMaker MV, and is harmless but annoying. Something about the way it stores certain files in the system causes issues if other RPGMaker games have previously been run on the same computer. Theoretically there are ways to force a game to use a LOCAL version of NW (I don't know why they didn't just make this the default), and I thought I had implemented them with some success in both games, but apparently the issues is still cropping up sometimes. Be sure you're using the most recent version just to give the best chance of avoiding this though.