First, please only post once. Posting twice causes extra work. How did you change IMAP to POP3? The proper way is to create a new POP account and then delete the IMAP account. If you attempted to change the IMAP account to POP, please start over.

HI David, I did not realize that my question would be seen twice. Please forgive me for any inconvenience.

How can I start over when Thunderbird does not let me do anything (per my question)?

1. first, if there are any messages in local folder or POP account involved, copy the profile elsewhere for safekeeping from windows file explorer.
2. then, delete the thunderbird folder at c:\users\<yourid>\appdata\roaming - that ensures a fresh start
3. now, either uninstall thunderbird or download and install latest version over it.

You now have a fresh, virgin, copy and it should start. If there were messages in original profile that you need, post back for more suggestion.

Hi David, Thank you for the quick reply. I have a lot of messages in my original profile to "carry forward". Assuming that I want to reinstall, what should I do to copy my messages, calendar, folders etc.?

Thank you in advance.

- IMAP folders will be automatically recreated - folders in Local Folders will be in profile at Mail\Local Folders\<folder name>file1, file1.msf, file2, file2.msf, etc. The msf entries are just indexes and will be rebuilt so are not important. - after you set up new thunderbird, install the addon, importexporttools NG, then do this: - highlight Local Folders - rightclick and select the importexport option to import mbox - select one of the files in Local folders for import - repeat process for all such folders - I am not well-versed on calendar and cannot advise there

There is the possibility that you could keep your current profile and see if it works. With the difficulties you were experiencing, I felt it safer to bypass it, but you might try the current profile and see if you can delete the account and recreate the account. That would keep everything intact if it works. You could try that first, installing new thunderbird over the top of current one and restart. that automatically would attempt to use current profile.