I have had a couple of instances with areas within a zone being non-transparent but also non-solid black wall. There were npc_types with race/bodytype combinations that gave this appearance. I solved the issue and this thread
http://www.eqemulator.org/forums/showthread.php?t=39907 talks about it a bit. The short of it is race = 240 and bodytype = 66 worked for me.
Not a clue if this is your issue but, if it is, then maybe this will be your fix.