Hello folks, today I have a same problem what title is suggested. I was worried when my WordPress visual tab of post was not working. Because of visual tab, “upload/insert” was also not working. I searched on the Internet, browsed wordpress forum but didn’t get actual solution. After lots of trial and error, I succeeded after doing few steps. Sometimes it happens when you update your wordpress version.
Here are few steps:
1) Deactivate all plugins. (This solution is present everywhere on the Internet). For me, it didn’t work. If you have problem like me then follow 2nd step.
2) Remove .htaccess file from wp-include folder.
3) Clear (delete) all browser cache and also use w3 total cahce plugin to remove all caches within your blog.
4) Still didn’t work? After that check your folder’s permission number through your cpanel- File manager or through FTP.
Hmmmm here I had a problem. When I was trying to upload some plugin, it asks me to make some directory/folder writable and by mistake I had changed the permission of wp-includes. So keep permission “755” for your wp-includes directory.
My blog only had a few posts when I encountered this problem. So I thought if I delete all database and reinstall wordpress, I will able to solve this problem but it didn’t work until and unless I changed my permission number to 755.
So guys Check Permission number of Your Directories before deleting all data, re installation of wordpress etc.
I did mistake so this would be my first post. I will repost my other articles again.