Realy need your help. I'm working with quite old Drupal 7 site and for some reason I cannot move the Main Page Content block to any different region. When I drag&drop it to the Header region (on block management page) and then click save, looks like it sucessfully moved, but when I go to the actual page I can see that it still located in the Content region.
Looks like something is preventing Main Page Content block from moving to different region but I don't know exactly what. I've updated Drupal to the latest release - no difference. I've switched to another theme - no luck.
What might be the problem? I'd be very gratefull for any idea.