Do you have a copy of the database before your upgrade atempt?

When you say you tried to restore the database, how exactly did you try that?

And you say you tried with both databases, so you have two?

Can you confirm they are sql files on your computer or what and where are they.

Further can you tell the difference from them i.e which version they are and how can you tell?

Hope all that is not too demanding :)

Sorry it's not clear \enough for me what you are doing.

"Hi, Well, I have uploaded a clean install and imported a copy of my mysql database backup, then opened the install with my existing back-up database. I copied over my media folder, and then changed all the skins to the Bootstrap skin. The site opened (https://blog1.lesduke.com) but I am getting the following error on every page:"

If you imported a database then you have no choice but the just install be default the imported database so why say you opened the install with 'my existing backup? What choice did you have? Or did you mention the same database twice.

You are also not clarifying which version of b2evo you are doing this with. For example the backup database would be for the old b2evolution.

So rather than answering my queries you have just another load of work that isn't clear to me, so I don't see how I can help without even more questions :(

OK I have a better idea of what you did but not enough info for my thinking, so i'll tell you what i have done on occasion.

I regularly keep a non zipped backup of the database as an SQL file by exporting from phpMyAdim via cpanel

Then if anything goes wrong, I ftp all the files of say b2evo6.11.7 that i was using when i backed up the database.

Then I drop all the tables from the database via phpMyAdmin and import the old SQL file.

This doesn't directly address your issue but it is so important to match the blog engine and database versions I start again from the previous working setup.

You can find the database version by reading the value in the database via Settings
https://forums.b2evolution.net/b2evo-version-and-database-version

I also have page to correlate database and b2evo version numbers
https://rogerlovejoy.net/blog/b2evo/database-versions
Ignore the not working part, that's just my site info that hasn't been updated.

So I hope this clarifies why I'm not sure of your efforts.

Hi,
Well, I discovered that B2E does not work properly on PHP 7.4. I had listed my version as 7.3.2, but my hosting service put it up to 7.4. SO, I was getting all those errors. As soon as I put it back to 7.3, it seems to work.

I also removed some old themes and widgets and now it all seems fine.

Thanks!