kstan

Check if you have mod_security enabled, and disable it if so.
 

Hi @kstan,
Thanks for letting us know the solution, I’m sure it will help others that encounter a similar issue. All the best with your community!

I just want to report that the problem has finally been resolved. In the end converting the database to utf8mb4 did the trick. I can't find it now, but I think someone at some point asked me why I hadn't done that. I replied that I intended to, but I wanted the other problem resolved first before messing with converting the database. Nowhere that I saw was utf8mb4 listed as a requirement to upgrade, but nonetheless, that's what solved it.
Thank you to everybody who tried to help. Much appreciated!

This usually happens due to disk issues on the MySQL server and/or corrupted keys/tables.
 
 

I would advise contacting your hosting provider for assistance here. Something is happening with your MySQL server if this is happening for all database tables when being attempted.

You're most welcome. Glad we could provide some insight at least to one part of your puzzle 🙂 . Keep in mind too that any upgrade you should take a full backup (files and database) before starting. This way, if anything does go wrong from your server to the software, you have a backup of your community that you can restore.

I deleted a cookie and voila, I was back in business. It then asked me to add a line to my constants.php, and after doing that, the rest worked smoothly.
Thank you for your help.

I deleted a cookie and voila, I was back in business. It then asked me to add a line to my constants.php, and after doing that, the rest worked smoothly.
Thank you for your help.

You would need to complete the upgrade or restore files. I’m afraid, there is no other way.