Steps to reproduce
After you log into the system you want to send a chat message to someone that isn't online.
You go to chat to see all online users and offline users to chat with
Not all users are visible on the right to start a chat with. Normally all users shall be available on the right side and the ones that aren't logged in should be gray
Work around to fix problem
Log out from the system, log in and then try again
Reason for problem
For some reason the system haven't received a correct chat roster via XMPP (the protocol the chat client and server uses to communicte), sometimes this can happen.