Re: Migrating Thunderbird personalized settings to another machine:

You failed to exit/stop thunderbird before making the copy of the folder, thus on restore it thinks there is another instance running.

Otherwise, there is a lock flag file somewhere.

I believe you are correct in your statement "you failed to exit/stop thunderbird before making the copy of the folder, thus on restore it think there is another instance running. I was not considering the Thunderbird I left running while copying the directory to USB. Thank you for pointing this out.