perhaps you could pot the contents of the profiles.ini file and a screen image of the file manager showing the path to the profile.

Thanks Matt. This has been solved this by following the steps to doublecheck the .ini file from this post: https://support.mozilla.org/en-US/questions/1123342

There are two drives on the new computer and the incorrect .ini file was on the data drive (I had been only looking on the OS drive), now that it has been updated with the correct profile all is working as it should.

Thanks, again for your willingness to help and your clear answers on the other questions I read in trying to solve this before posting my question.

just a warning for your own sanity. Never change the local directories in account settings.

They fragment the profile data and make the next move a nightmare with absolute references that usually no longer exist.

Thank you. I will make a note of that. I hope not to migrate for several years, and maybe by then some of these accounts can be retired. But, at the moment I need to access old emails that are in no-longer-hosted email accounts, so this profile is the easiest way to access it (aside from an old slow machine that is painful to use - and not portable). The rest of the active email accounts are IMAP, so are easy to add to a new machine.

In the future, if I still need those old emails, is there an easier way than moving the profile? Could I just copy and paste the specific email folders to a new profile?

Vini1 said

In the future, if I still need those old emails, is there an easier way than moving the profile? Could I just copy and paste the specific email folders to a new profile?

I think I cover that here http://thunderbirdtweaks.blogspot.com.au/p/blog-page.html

Please tell me if I do not. A technical writer I am not.