During migration to another host I came across 2 Vms that gave an error :" Operation timed out:The VM failed to resume on the destination during early power on".
Restarting management agents on the hosts didn't help. Finally one of my colleagues noticed that the VM names had more than 32 characters in them.
So we got the users to truncate the names to less than 32 characters, then storage-vmotioned them back and forth so that the vmfiles on datastore are re-named and then the migrations worked beautifully.
Hope this helps some one.