Jean Rochon

Go to wordpress dashboard of your site.
Choose Extensions on the left side menu
In the list of extension spot CKEDITOR and desactivate it.
Maybe you not have CKEDITOR, but other extension, so go in try and error mode and desactivate another extension and see what’s happen.
Good luck.

Hello Mayur77,
I had just disable extension CKEDIT and that solved my problem. But it’s not normal.
I wrote to CKEDIT support but never received a feed back. Maybe it’s because I’m using the free version.
I hope that will help you. Let me know
(excuse my bad english)
Jean

Thank you very much for your answer but I don’t understand why it was working before the 4.8 version of wordpress.
Well, you will have to help me. How can I use and where I write the debug code “define( ‘WP_DEBUG’, true );” and other codes.
Thank you for help.