Always HATE it when this happens. Been tinkering with FS's for over 35 years and then some simple bit of scenery won't install... Grrrrr...
Maybe it is because I also HATE the Addon Scenery folder and refuse to use it in general. I don't like the 'garbage dump' folders where you can't find anything back in, so for FSAddon - and most of my other add-on sceneries - I just make separate folders, preferably OUTSIDE of FS(X). For some reason only Misty's will install.... as soon as I try any of the others though, FSX just doesn't let me click 'OK' after adding scenery.
Also, the Misty's that I installed seems incomplete. No hangars, smoke floating in the air somewhere.. just a few static aircraft and green trees.
So I guess the EZ_1 stuff doesn't go well either on my installation (I put that in the Addon Scenery folder - grudgingly ...