Problems creating submenus in TwentyTen and TwentyEleven

Hi. Are having some problems with submenus in Themes TwentyTen and TwentyEleven. I am using multilevel menues in these themes, and have several submenus. Suddenly, I cannot create new submenues. Every time I try to save the multilevel menu after having created a new submenu, the submenu is “moved up”/”moves out left”, and the submenu becomes a new “main menu” instead of at submenu. You can see my sites at: https://www.n?kkvi.dk(WP version 3.1) and https://www.dm-alrid.dk (WP version 3.3.1.). Are having the same problem in both versions. Can anyone help me? Any tips are greatly appreciated! Should add, that I’m a new WP-user :-).