[in use] error

I’ve been using eM Client for a few months now.  I have found that many times when I open the client, it doesn’t bring in any new email messages, though I know there are some on the server.  In checking the log, I find this message: “11:04:00 AM Twc (georgefj) [POP3]  Connecting: Login to POP3 server failed due to the following reason: [IN-USE] account is locked by another session or for maintenance, try again.”  I may have to wait a couple of hours before I can bring in the new messages.  Any thoughts on what is going on, or what I need to do?