Symptoms
You see a red dot in the upper right-hand corner of the sign-in screen on your Mac or you receive the following message:
Network accounts are unavailable.
Cause
Your Mac is joined to a domain, and network access is needed in order to sign in to the domain. When the computer first starts up, the wired network connection may not be active immediately.
Resolution
Wait a few moments for the wired network connection to initialize.
Outcome
After the network connection is established, the message will go away automatically and you will be able to sign in to your Mac.