Renamed subdirectory, got 404 message

As per previous forum answers here in General Settings I changed the subdirectory name from /wordpress2 to /blogsitestudio, in the WP address and Site URL, but when I tried to save changes, I got a 404 Not Found message. Ok, that was expected, but it still never saved.

I changed the subdirectory folder name to /blogsite studio, again per instructions, and that was fine. Entering the address in the browser brought up the correct pages, so that was fine.

My problem is with WordPress. It won’t let me save the changes in General Settings or navigate away from that page. What did I do wrong and how do I get WordPress to keep up with my changes?
Thanks for your help.