My heads updide down, its getting kind of annoying, if somone can please help please do, i restarted the server many times, im using mclawl, and i tried setting up a newone, delete all of my maps, still the heads of everyone are screwed up

PLEASE if you could help me thanks

Heres the link to my server:
http://minecraft.net/play.jsp?server=aa0d14907b806a159b9ff5a71208a267