One client working, one not working...
 

I play a few toons on one laptop and I haven't had any issues until now. My setup is playing my main tank on one client with the graphics, etc on and I play the rest on a seperate client which was copied directly from the original (Underfoot) so the files should be the same aside from the setting, which are all turned down and in stickfigure mode. I haven't had any issues so far, but for some reason on my main client I'm able to zone into Plane of Sky without issue but on my alt client the game crashes when I try zoning in there.

I've tried copying the zone files from the working client to the alt one which hasn't worked...any ideas?

you could try using Win EQ2 to load all your boxes through 1 client. it allows you to keep seperate INI files for each window and each character which would allow you to keep the gfx turned down on all but your main etc.

http://www.lavishsoft.com/

ISBoxer would also do the same thing but its not free, 10 bucks for a 3 month subscription and it would also depend on the server rules, im sure there are some servers out there that would frown upon use of isboxer since it allows some features that are similar to "that which will not be named" :P

as for the specific issue i honestly have no idea, i had something similar happen while running from the same client, maybe try removing your character/ui INIs from your second client and starting fresh - could be an issue there?