Cannot edit menu anymore

Hello, for some reason I cant edit my (primary)menu anymore especially the last menu-button. If I try to make a subitem under this last button (and save) it switches to a main position or it shows not at all after saving….this action also unmarks the primary menu, completely messes up the whole menu. When i delete the subitem again en mark “primary menu, the menu works (shows fine)again….i tried with disable the plugins but no luck there……..its driving me crazy !! HELP PLS ;-)

ps: I made a new second menu and that seemed to work fine, but when i tried to save it, all subitems under the new menu were gone too. seems the problem occurs now on both menu’s