Tried to log on some time ago, and there it said the servers were too bus with too many players on. Never seen that before.
if you go https://www.everquest.com/home you can check the servers population. It looks like "white" is people on, that one server shows pure "white" so I am guessing that server is full. Coirnav is the server that looks like its full.
Yup, this happens when we have a large volume of players logging in across any number of our titles. It will typically resolve itself after a few minutes when the login server is not overloaded.