I had some MZ games running on 5.1.x I believe, but I run 0.48.4 on my own in MV, but if that is the cause, than it sucks really.
I hope it wouldn't be that worse, but I can see why it throw
it the error like that, I go do some digging on the nwjs 0.74.
EDIT:
so far I can read, 0.57.1 can work on win7 and 0.72 can work (final release for win7 support).
so if you can set it to 0.72 for me to test, it shouldn't give the error as well, but it also have the
most release version for your game for win7 users :) (hopefully).