Did you happen to leave non-PNG image files in your project folder, particular any raw files? I don't know how MV handles it but I know VXA has this thing where if you leave, for instance, a .ase file (used for Aseprite) alongside the PNG version, VXA's interpreter will prioritize the .ase version for some reason and crash the game when trying to load it. And this only happens when the project is encrypted.
I don't know if MV's encryptor does the same thing but it might be worth checking to see if your image files are the wrong format.