Updating error there was an error performing the update mac
If an i Phone user sends a text message to another i Phone user it is sent over the Wi-Fi, mobile internet data or any other form of internet access rather than being sent over the cellular or wireless service provider's network and thus saving on the cost of sending a text message.
Go to ~/Library/Preferences/ and delete all files and folders beginning with the following prefixes: com.apple.ichat com.apple.icloud com.service com.com.apple.identityserviced com.apple.imfoundation com.apple.imessage com.apple.imservice com.apple.madrid com.apple.com.apple.imagent.plist com.apple.security You may not be able to delete some of the above plist as they are already in use by the app.
Check if your Mac has the correct date and time and set to synchronize automatically with the right Apple's server.
Click on Apple icon on the top left hand corner and select system preferences Click on Date and Time Tab and Select the checkbox for ”Set date and time automatically”.
If the i Message works and you do not get any activation error then restart in normal mode and try again.
If you still get activation error during login then move to the next step.