I am using Thunderbird to connect to a personal POP & SMTP server. I have recently migrated to a new desktop and moved the old profile folder to the new computer (so I would keep all the emails). Everything was transferred successfully, including the profile settings.

When I open Thunderbird, I am asked for my password and it all goes well if I enter it manually. If I check the "Use Password Manager to remember this password" box, I am met with a "User to server X with username and password failed" - error and a "Sending of password for user did not succeed" - error. I am entering the exact same password in both cases, yet it only fails when I try to save it.