Is this a 'master password' or the password for a particular email account? And does the error message appear when you try to log in to download your mail or when you have composed a message and try to send it?

It is not the master password. It happens when I try to download my email.

It's a gmail account

When Thunderbird fails to connect to the server you can get a generic error message which says that your password hasn't been recognised. Sometimes that is exactly the cause but sometimes it's because of another reason, although the message (unhelpfully) is the same. There's an article here which offers some troubleshooting suggestions: https://support.mozilla.org/en-US/kb/cannot-receive-messages Try those first, as a start.

I went to the mozilla support page and it suggested I go to Google's web page for my gmail account. I was able to reset my password, and the problem was solved. Thank you very much.

Well I have the same problem as all the above but have been unable to get TB to open my email. I changed the password on my MSN account and can access the email in Outlook but when I give TB my password I get the following error Sending of password for user odehart_5@msn.com did not succeed. Mail server pop3.live.com responded: Authentication failure: unknown user name or bad password. [Error="ProxyNotAuthenticated" AuthResult=0 Proxy=CY1PR15MB0457.namprd15.prod.outlook.com:1995:SSL] If Outlook works how come TB won't?