Ah come on - you have to provide us with more info than that.. - if you want some help...
Versions?
What storage?
What do you hostd / vmkernel logs say?
Maish
VMware Communities Moderator
My Blog - @maishsk
Co-Author of VMware vSphere Design
Maish Saidel-Keesing • @maishsk • http://technodrone.blogspot.com • VMTN Moderator • vExpert • Co-author of VMware vSphere Design