Have you looked in the windows task manger and killed any running task?

Yup, I have to go there to stop Thunderbird, otherwise the error keeps returning, just saying OK doesn't stop it. As soon as the error comes up just go to taskmgr, nothing else works. I also tried renaming both profiles with -old after them so it will rebuild a new one. The error returned. Going back to -profilemanager they retained their names, the -old was gone.

re : I don't have a profile.lock file to delete.

That does not sound correct. Stop/check Thunderbird is not running via task manager.

Do you have a 'parent.lock' file in either of the profile name folders? I'm assuming no.

If you have a backup then copy the 'parent.lock' file from backup and paste it into the 'profile name' folders.

Alternative. Try this: Create a new 'parent.lock' - right click in 'profile name' folder and select 'New' > 'Text Document' Set filename (all lower case) as: parent It will create a file called parent.txt Then rename that file by changing the extension from .txt to .lock and ok it. You will probably get a warning but do you do want to do it.

Then start Thunderbird and report on results.

Thank you for your help. I created the parent.lock file as you suggested but unfortunately Thunderbird responds the same. "Thunderbird is already running..." Is this possibly a registry error?