Error attempting to migrate VM between ESXi 5.1 hosts - Managed Object Reference xxxxx refers to object that no longer exists ??

I am attempting to test a vMotion migration between two ESXi 5.1 hosts that do not have shared storage. The compatibility check for the Hosts is successful, but when it goes to the compatibility check for the datastores, I receive the following error:

ManagedObjectReference: type = Datastore, value = datastore-1192, serverGuid = XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXX refers to a managed object that no longer exists or has never existed.

Anyone have any ideas what might be the problem. I have checked the folllowing so far:

Networking is ok.

Hosts are licensed for VMotion and Storage Motion.

Both datastores are local to the Hosts.

Each host has two datastores:   esxname-datastore1  &  esxname-datastore2