The error "Failed to connect to engine" is caused by the LogMeIn Hamachi Tunneling Engine either failing to start, being in an error state, or being blocked by anti-virus software. If your anti-virus software is reporting/blocking Hamachi-2-ui.exe, you will need to add an exclusion for the Hamachi-2-ui.exe program. Please consult your anti-virus software documentation for assistance with adding an exclusion to the allowed list.
On Mac please try the steps posted by @cbrough
Our solution was:
hopefully this helps others as well.