If you’re like me, your Mac server is buried in a hole somewhere in your house and you don’t necessarily know where a monitor that will just port over to it so you can physically login. If this is you, you generally activate screen sharing when you need access directly; this time though, it’s not accepting your password. If for some reason this has just squashed out on you, don’t fret, ssh into your server, change to a root (sudo bash) and execute the following…
sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -activate -configure -access -on -users admin -privs -all -restart -agent -menu
