When mov­ing a VM, you might see this error mes­sage “Migra­tion from <server.> No guest OS heart­beats are being received.  Either the guest OS is not respond­ing or VMware tools is not con­fig­ured properly.”

The tools have to re-establish their sta­tus to ESX, and then to the Vir­tual Cen­ter.  The warn­ing won’t pre­vent migra­tion, but you should prob­a­bly wait long enough for the rene­go­ti­a­tion to happen.