Symptoms

Parallels Desktop displays the following error:

 

The operation could not be completed due to a critical error

Cause

This error message can be caused by several reasons:
- the Hypervisor driver failed to open
- Physical memory manager (PMM) initialization or update memory settings failure
- Other reasons.

Resolution

Check that Hypervisor is running
to do it open Terminal.app on your Mac (/Applications/Utilities/Terminal.app) and issue the following command:
 

kextstat | grep prl_hypervisor

If the output of the above-mentioned command is empty try to reboot your Mac, then check if Hypervisor is running using the same Terminal command.

NOTE: Please print these instructions from File ► Print browser menu for your convenience

If it's still not running please reinstall Parallels Desktop.
If the issue remains please report this issue to Parallels Support Team.