Internal error: xenopsd internal Error: Hotplug.Device_timeout

This is the error message we sometimes get on a XenServer 6.5 fullly patched hypervisor.

"Internal error: xenopsd internal
Error: Hotplug.Device_timeout(_)"

The VM's will not start and they get the error. I hesitate to upgrade some of our older hypervisors until we figure out the fix. Please note, that there were no external drives or virtual CD loaded in the VM when the server had this problem.

Rebooting the affected hypervisor seems to be the only way to fix the issue. The biggest issue we had for rebooting a 'failing' node was you can't migrate VM's off of it - migrations, starts, stops - all fail.

Any help would be greatly appreciated.