Sending of password for user {where my e-mail address appears} did not succeed.  Mail server pop.windstream.net responded: [IN-USE] account is locked by another session or for maintenance, try again.

When trying to access e-mail using Thunderbird I frequently get the following message: Error with account Home account Sending of password for user {where my e-mail address appears} did not succeed. Mail server pop.windstream.net responded: [IN-USE] account is locked by another session or for maintenance, try again. When his happens, I then get a window with options "retry", "change password" or "cancel" Using retry or change password just results in repeated messages. Cancel returns me to Thunderbird but without access to the server for new messages. This error seems to happen randomly with increasing frequency. Sometimes, after a short wait, connection is made. Other times a long period without access occurs, then suddenly access is possible. Can anyone explain this message and its source. Discussions with the ISP provider, Windstream Communications, results in assurance that the the mail server is working and not the source of the error.