Windows 10 op system. Thunderbird has worked for years. I have two accounts set up for same ISP server. No changes to account settings, no new programs installed, virus scan says all OK. Getting email OK this morning. When I try to get messages, or send a new message, I get error "Login to server mobile.charter.net failed. Retry. Enter new password. Cancel". If I select Enter new password, I get the old password showing in a box, with the 'remember password' box unchecked. I have logged in to my ISP account and got into emails using password, so it seems the server is OK. I have verified that all account settings match those expected by my ISP. I have deleted all passwords in TBird several times, restarted, entered the correct passwords, and no change to error message. Tried rebooting computer = no change. (When I rebooted the first time, TBird installed updates.) To restate. NOTHING was changed on computer or in Thunderbird before this problem popped up. Anyone know definitively how to fix this? Thanks