troubles after moving websites

Hi i created site on server – all running smotth and dont have any troubbles . moved it to final place and domain. changed all references in posts and other places to new site but encountered some errors

when i try add anything to menu it return blank page http://gentlehouse.pl/wp-admin/nav-menus.php it dont save anything …

also sometimes after admin login in dashboard also return to blank page but after reloading page it works …

it still works on old site