The same account is logging in twice
What it looks like in your log
You logged in from another location
What causes it
The server saw a second login for an account that is already connected, so it dropped the older session. A ghost session left behind by a crash or a timeout looks exactly the same until it clears.
How to fix it
If the player cannot get back in, wait for the old session to time out or restart the server to clear it. If it repeats constantly, look for a proxy in front of the server sending the same player twice, or an offline-mode server where two people share a name.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log