xend Error: Acquire running lock failed: 256

Recently I encountered this issue in OVMM 3.2.9  while starting a vm with

xm create <vm.cfg path>

The reason behind this found was : the vm was not shutdown properly  and the lock file is still there even if VM is down.

So the places to look at :

Look at the log file and if the lock file is present under /var/run/ovs-agent/ with the id of the vm which is not starting, just delete the lock file and then VM will start successfully.