Comment 2 for bug 1626334

It seems that the reason of the releasing failure is related to this:

Failed to power off node - Node could not be powered off: Failed talking to node's BMC: 10.244.192.131:443 is not a VIM server Wed, 14 Sep. 2016 10:21:34

I've searched through the MAAS code and "is not a VIM server" doesn't come from MAAS. It actually comes from python-pyvmomi: https://github.com/vmware/pyvmomi/blob/master/pyVim/connect.py

This error seems to happen when the client tries to connect to the server and it cannot find a SupportedVersion of the API.

What may be happening, however, is that the client cannot actually connect to the vCenterAPI, which could be creating the issue.

So I'd say that this is related to connectivity issues between the Rack and the vCenter.