mmm the building cass might be cause your missing the tag in building info,
or building classinfo.xml,
bout why it froze idunno,
i think you should have started the build on the ff files,
try to merge it agaipart by part and check if it works, its realy hard to guass wheres the bug now when you have it all on ff,
start with adding just thenations to the ff mod, then try the mod see if its ok, then move on to the units, and so on.
thats the only way to track the cuase i belive.