Main Menu disapear

Hi, I have a problem with the menu/submenu I made by admin section of the theme, I have try this in 4 or 5 different theme.

If I setup the menu in a subdomain like http://dev.lesnouvellesrss.com the menu work like a charm.

If I setup the same menu at my website http://www.lesnouvellesrss.com I can use navigate inside a couple of times .. if I change or check with Firefox, Safari, Internet Explorer I lost my menu/children menu somewhere and only 1 or 2 link stay in the menu.

When I go in admin menu I got this kind of error ( translate originaly in french )

The identifier given for this object is not a menu entry.

Thx for the help!