TB91 is a whole new developed version. Does not fully support old profiles. Creation of a new profile is required. Then you can import old emails, calendars and contacts. Since import export tools ng is no longer supported in TB91 use Mailstore application to import emails in TB91.

TB91 is a whole new developed version. Does not fully support old profiles. Creation of a new profile is required.

This is nonsense. Existing profiles used with TB78 are supposed to work also with TB91.

I installed TB on Drive D (D:\Program Files (x86) and put my old profile in D:\ThunderbirdProfile. Then I opened profile manager, established a new account "OldProfile"

I don't understand what that means. Using profile manager you obviously can manage profiles, but not accounts. What is the contents of your profiles.ini file?

Here are the contents of my profiles.ini file: [Profile3] Name=default-release-1 IsRelative=1 Path=Profiles/t8prah4j.default-release-1

[Install746F856C10C5FA7C] Default=D:\ThunderbirdProfile\jy0ahqrm.default Locked=1

[Profile1] Name=default IsRelative=1 Path=Profiles/pgut6goc.default Default=1

[Install1923D9E7A3A65A99] Default=D:\ThunderbirdProfile\jy0ahqrm.default Locked=1

[Profile0] Name=default-release IsRelative=1 Path=Profiles/bby7ug87.default-release

[InstallC8D51EDE300B8FBD] Default=D:\ThunderbirdProfile\jy0ahqrm.default Locked=1

[General] StartWithLastProfile=1 Version=2

[Profile2] Name=OldProfile IsRelative=0 Path=D:\ThunderbirdProfile\jy0ahqrm.default

There are 4 profiles in total in your profiles.ini. I suppose this is the one you want: [Profile2] Name=OldProfile IsRelative=0 Path=D:\ThunderbirdProfile\jy0ahqrm.default

With which version of Thunderbird was this profile used before?

Is this the profile you use when starting Thunderbird? To check use the Menu Button in the top right corner - Help - More Troubleshooting Information - about:profiles

Make sure the desired profile is set as the default one.

Yes [Profile2] Name=OldProfile IsRelative=0 Path=D:\ThunderbirdProfile\jy0ahqrm.default is the profile I want to use. I have no idea what version of TB I was using when I started this profile. There are probably 12 or more years of old messages in the profile. Every time TB said there was a newer version I upgraded. I ended up with v. 91.0.3. If it would simplify things I'd be happy to delete all the other profiles since I use only one. When I get to About Profiles as you suggested, I have the option of deleting profiles. Should I delete all but Old One (jy0ahqrm.default)?

I had this issue as well, I got around it by copying the contents of the original profile folder into the new profile folder (overwriting any files that exist already in the new folder) and then opening thunderbird worked again.

I have no idea what version of TB I was using when I started this profile.

Well, what I meant was the version of TB used prior to upgrading to TB91. If that was TB78.* then there should be no problem.

Every time TB said there was a newer version I upgraded. I ended up with v. 91.0.3.

There is no automatic upgrade from TB78 to TB91. So installing v91 must have been a deliberate action you started.

If it would simplify things I'd be happy to delete all the other profiles since I use only one.

That's something only you can decide. It probably would be a good idea to clean up profiles not in use anymore. However, make sure to backup any data you may want to keep prior to deleting old profiles.

As said before, make sure that

• Thunderbird starts with the desired profile, and
• the desired profile is set as the default one.

You can do all that via about:profiles.

I deleted all but the one profile I need, double checked that TB was pointed at my old profile and still all I get when I open TB is the Home and Account Setup Tabs. Maybe I should drop back to an earlier version of TB?