Problem with the primary menu

Hi,
i´m pretty new in using drupal, started about 4 days ago.
Now built one site using another theme, but now i would like to use your theme greeny_blu to have a second working theme.
My problem is, that after klicking on two or three menu links the link always gets one "node" more in the adress, so i always get the message "page not found".
Do you maybe know where the mistake can be?
Maybe you have a better imagination if you can see it on your own: www.just-websites.de/icedanceberlin
of course now there is nothing done to let the content nicely fit into your template, because first i need to know, if i can solve the problem with the menu, so dont be upset if you see how ths site looks right now :o))

I hope you understood everything, english is not my first language, but i try my best:o))
would be great if could help...
Flo