Thanks esmi for the advices but none of those did not seem to make a trick. BUT! The problem is now solved and it went like this:
- I re-uploaded the wp-admin and wp-includes couple of times from different versions.
- Switched theme, browser, computer, nothing.
- Deleted everything I could think of with CCleaner, even deleted the plugins from WP, still nothing. Etc, etc. My hair started to turn gray..
Then I started do what you do when you got a situation like this. Act random. I had previously of course checked the user page "take off the visual.." but I went back to check it again just in case and then I noticed something suspicious. The button was "old" looking and it got white area around it. So I started to check and uncheck that button couple of times but still nothing. I was devastated.
Then I got back to CCleaner and run it. Nothing else to do.. And after that it worked! Now the button looks "new" again.
So, how's this possible?
At the CCleaner I did not however deleted the forms field memory since I need them in my job and I did not thought of it cause I thought it was in basic some java cache related problem. The user page has ofcourse a form in it..
So there were these two things which maybe simultanously caused the problem. But now it is solved and I can breath again. Thanks!