Error message again!

I have once again ran into trouble when adding pages to a site. When I add new pages into the menus everything is fine until get to around 20 or so then I get “internal server error message” and the menu area then wont let me change anything without getting that error.

Can anyone help, this is very frustrating as second time I have had this issue without being able to get an answer why its happening.

Appreciate any help!