Have you tried creating a new profile then pointing it to the old profile folder?

I'm afraid I don't understand what you're suggesting. I could create a link under a new name that points to the old profile folder, but that wouldn't change the content of the profile to make it compatible.

The current Thunderbird version in windows is 68.6.0 (32 bit); in Ubuntu Linux it is 68.4.1 (64 bit). The windows version is working as expected, and is using the same profile as before. When I use the profile manager to attempt to start Thunderbird in Linux with that profile, I get the error message: "A newer version of Thunderbird may have made changes to your profile which are no longer compatible with this older version ...".

So it appears that when I updated the windows version, it changed the profile structure, and the most recent Linux version is not compatible with that structure. Does anyone know, can we expect a new Linux version to be released that is compatible with the changed profile structure, or is the 68.4.1 Linux version really compatible with the new profile structure, but the error check is faulty?

That's Thunderbird's downgrade protection, and was introduced in version 67. A download of 68.6.0 for Linux is available here https://www.thunderbird.net/en-US/thunderbird/all

Thank you. I was able to install the new version and run it from the directory in which it was installed with the shared profile. But perhaps you can help me to clean things up a bit.

The newly installed version is in a /tmp sub-directory. The old version is in /usr/lib/thunderbird. When I try to start Thunderbird from the Application Launcher, the old version is started. I'd like to get rid of the old version, have the new version installed in /usr/lib/thunderbird, and have the Application Launcher start the new version.

I tried moving the old version to usr/lib/thunderbirdOld as a temporary measure, and doing a recursive copy of the new /tmp/.../thunderbird version to /usr/lib/thunderbird. But now when I try starting Thunderbird from the Application Launcher, I get the error message "Could not find the program 'thunderbird' ". What should I do to get it set up properly? Should I reinstall the new version in usr/lib/thunderbird?

Use the Synaptic Package Manager to update the packages database. The latest version of Tbird is probably already added to the official Ubuntu repositories, but if it isn't, uninstall the old version then check out https://sourceforge.net/p/ubuntuzilla/wiki/Main_Page/

The problem was that the latest version of Linux Thunderbird is not yet in the Ubuntu repository, and the version currently there is not compatible with the user profile of the latest Windows version.

I have had this problem before, and I fixed the issue by putting a link from /usr/lib/thunderbird to the install location. Note that the install location cannot be /tmp/sub-directory because that is cleaned out each time you reboot. The install should be in /home/<your user name>/thunderbird .

NOW!!!! I HAVE ANOTHER KETTLE OF FISH TO FRY.... [ Same issue ]

My dual boot system worked well for a while, and then (today) the WIN10 version corrupted the shared profile located on an ext4 partition that I share between Linux and Windows with a windows program that provides access to ext Linux partitions. The corruption made the Linux Tbird unable to use the shared profile. I identified the corruption as losing an entire group of file folders and a second email account. I did not update Tbird on the WIN10 O/S or the Linux O/S. today when this happened because both were operating BEFORE TODAY without problem. Note that the WIN10 Tbird can use the corrupted profile and the Linux Tbird cannot.

BTW, I converted the shared partition a year ago from FAT32 to ext4 because WIN10 was regularly putting various boot options on the FAT32 partition so Linux would not boot. I had removed them as they came up, but they kept reappearing with every WIN10 update.

Added info

Your web page calls this screenshot of text I tried to use unacceptable:

"Links are not allowed in the forums"

Really?

Hi Michael,
Stans' post was marked as the solution by the person who asked the original question (wheintzelman). Your issue may have similar symptoms, but it is likely a different cause/solution. You should use https://support.mozilla.org/en-US/questions/new where volunteers can get more details about your setup.

Because this thread is solved and more people might start using it for their own questions, I'm going to lock it.