I can't see how FS could cause that problem when there is no Vert error. If the morph loads, there will be a dial, usually on the bottom. But to make sure it is not FS why not open the .obj, the one from the exported V4 head so everything lines up right, in UVMapper. It will show the head, resave the .obj and load that. If there is no head when you load the morph in UVMapper, then you might have a case to blame FS.

In the meantime I will start up FS and export a V4.2 head and do a test for you right now. Will be back in a few with the results.