iMessage stopped working.. Contacts are shown as red now This problem has been seen on mid-2012 MacBook Pros on Mavericks and on late-2014 Retina MacBook Pros on Yosemite.

One day while using iMessage on the Mac, all the contacts turned red and messages failed to send, immediately returning a "not delivered" error. It also reported when trying to resend the messages that the contacts were no longer associated with an iMessage account.

Things that didn't fix this behavior:


Deleting the com.apple.ids.madrid
Removing the Apple ID information from my phone, turning off iMessage on both of the devices, and placing my iPhone in airplane mode for several minutes before turning it on logging in again.


Could someone help me figure out how to solve this?
One way you will get the red contacts is if the iMessages account is not enabled.

Go to iMessages's preferences. And make sure the enabled check box is ticked.

You Will also get the red contacts if you are not signed in. 
If that is the case you will need to sign in to see the enable check box.