New Parallels Desktop 12 upgrade: VM won't launch

OK... this isn't very reassuring. I've just upgraded to Parallels 12.0.0, from the latest version of Parallels 11, on my MacBook Pro (Retina, 13-inch), running El Capitan 10.11.6. The laptop is connected to an external monitor via HDMI and I usually run it with the laptop lid closed. Before upgrading, Parallels ran my only VM, a Windows 10 machine, without a hitch.

After upgrading, the VM refuses to launch, or rather: it launches but I get nothing but a small window with the VM's title but no visible content in the window. Activity Monitor says that the VM is using 90% of my CPU load, so *something* is happening. But the window sat there, blank, for 45 minutes before I closed it. Did this twice without a different outcome.

So I'm stuck now, with a VM that won't, um, M.

Any advice?

 

One more thing. Just before the VM appears to hang (?) I get a little animation in its window that says "[VM name] starting..." And this: on a hunch, I tried running the VM while the laptop was not connected to an external monitor. No difference.

 

Can you post a screenshot please? Also what is your hypervisor setting? (configuration < hardware < cpu and memory < hypervisor)

Here is the kb. Article on this issue. Kind of a long workaround but until the engineering team solved the issue this will get you running.
http://kb.parallels.com/en/113823

 

Hypervisor setting is "Parallels" (the default)? Yes, the workaround will be long and time-consuming. Very frustrating.

 

If you don't mind try the apple hypervisor and if it still won't start try to select reset from the actions menu then restart VM.

 

Changing to the Apple hypervisor seems to have fixed things (?) The VM is up and running. Will keep an eye on it to see that all remains well.

 

ok good deal