Message: Failure creating VM datastore lock Host: ESXHostNameha-host VM: MVName
After investigating, the root of the issue was that the ESX host had run out of memory - there were too many VMs running on this host. This was keeping the VMs from quiescing long enough to get a good snapshot. When they would try, the memory would spike and balloon all over the board. After thinning out some memory, the problem disappeared.
This particular client is growing faster than they were paying attention to, hence the increase in memory utilization across the board.The client is ordering more memory for all the hosts in their cluster and looking at ordering another host or two so that they can get back to N+1 (where they actually started at).
Here's some books that should help out:
VMware vSphere 4 Administration Instant Reference
VMware Fusion 3
VMware Cookbook: A Real-World Guide to Effective VMware Use