I always kept my wordpress up to date.
As the 2.9 came up, I updated by auto-update without erros.
But suddenly my "Create New Article" Function didn´t work anymore.
So I used my backup to continue using the previos version.
Now I updated to 2.91. Again with Auto-update, again without errors.
But again I get a Malfunktion when I try to create a new article:
Fatal error: Cannot redeclare class services_json in /var/www/(*Webspace*)/html/blog/wp-includes/class-json.php on line 114
I don´t have a clue what to do now to get 2.91 running.
The Blog itself seems to keep running and working for users. But I can´t create new articles and maybe some other things. Dashboard opens normaly!