After El Capitan update, I cannot sign in to anything with my Apple ID: '"This action could not be completed. Try again" I updated OSX last night to El Capitan and after the update, and restarting my iMac(2014) a few times, I cannot sign in with my Apple ID. 

The initial restart gave me the error: "This action could not be completed. Try again." I assumed I had forgotten my password, so I went through the procedure of resetting my password. I was then allowed access. 

When I then tried logging in to another service requiring an Apple ID (Mac App Store in particular), I get the error "This action could not be completed..."

Restarting my machine does nothing. Should I revert to an older version of OSX?
Execute the following commands in Terminal:

sudo mkdir -p /Users/Shared
sudo chown root:wheel /Users/Shared
sudo chmod -R 1777 /Users/Shared