It works for me now. I downloaded the new 4.5.6 from the site, exported the maps, objects, and monsters from the older project, imported them, added my custom scripts and inputs (with the old project open in the old version of NESmaker for easy reference), manually updated palettes and imported the Famitracker song txt. You also have to copy your assets over to the new graphics folder after you create the new project. I did this before importing the maps but I don't think it matters when.
It loads, music works, and the previous beta glitch at the scroll seam is also fixed.