cant add any pages to my custom menu…

Hi,

I am having a big and very strange problem with my wordpress site.
I cant add any extra top-level pages to my custom menu.
I never had this before, is there anyone who knows what it might be??????
I CAN add posts to the top-level of my custom menu, and there are pages on it already which I added months ago.
check out my site here
I really hope anyone of you got a fix for me
thanks in advance!

[ Please do not bump, that’s not permitted here. ]