Bad Request ::: error message

Hi, I’m sorry if this is not the right category for this post.
That’s what I propose today, a weird problem that none of my friends have ever seen!
If I go in the menu settings> permalinks and select one of four settings when I save changes I get this lovely error message:

Bad Request
Your browser sent a request this server That Could not understand.

Now I noticed that this problem happens to me even if I change the plugin “Under Construction”.

I have not found anything on the web to solve the problem and I’m beating my head for several days now, I hope you are able to help me solve this problem as soon as possible!