I will stay with this, it works and I'm happy. You're right, I should make a record of all my steps and messages I got there. Next time I'll certainly do that. And another funny thing I've got - now I have an invitation on admin page to upgrade the latest version 2.0.5 (even though I have 2.1-rc1). ...

It is strange! I realized that my PHP had ver.7.0 when I was trying to downgrade s9y in order to catch a working configuration (as I said I'm not a programmer, so I use a method of scientific kick). I was positive that my site is on PHP5.6, but apparently it was changed and maybe that's why I got in...

Ok, everybody, I fixed it
I changed php from 7 back to 5.6.30 on s9y 2.1-rc1 and it started smiling to me again.
I still don't understand how this tagging works, though
Anyway, thank you for willing to help.
Be blessed everyone!

Hello everybody I hope everything is fine with you. I've got a problem. I installed some plug in something like "Tagging of entries" or something I don't know, I cannot check cause my site is down. It was there quiet a while. After that I decided to open new category and realized that ever...