Thunderbird suddenly started asking for my password, but does not accept it. (Web mail works fine with the same password)

Thunderbird starting asking for my password. I know the password, just have not been asked for years. After typing in password keep getting message 'Sending of password did not succeed. Mail server mail.intergate.com responded: dmanns logon failed ' however, I went to Webmail.intergate.com; was redirected to http://email.1dial.com/webmail/Login.aspx. Can get email from webmail just fine (same password), just not via Thunderbird. Have already run two anti-virus scans. Have deleted the saved passwords and re-entered them as the program asked for them and renamed key.db & signons.sqlite (Read this in a forum on the web) and they rebuilt themselves. Still can not get email via Thunderbird.