vsphere HA Virtual Machine failover failed

Hi,

There are 3 ESX hosts in our cluster.  One of them (say Host3) just exit Maintenance Mode.

Then we change the DRS setting to aggressive and run HA reconfigure on the other two ESX hosts (Let us call them Host1 and Host2).  We just want to migrate VM to the ESX host that just exit from maintenance mode.

However, we find that all VM on a particular ESX host (Host1) and one VM on another ESX Host (Host2) get the error message "vsphere HA Virtual Machine failover failed".  We would like to seek your advice what are the potential causes of that error message ?  Which setting in cluster control the behavior ?

Thanks