Dyn. Menue Problem

take a look at
http://www.palm-touristik.com
the navigation under -reisen- doesn't stay open after choosing one...
so the procedure of klicken your way through begins again...
is there a way to change that???

also there is that weired behaviour, that the menue is open when the page is loading??

FF javascript console says
Error: event is not defined
Source File: http://www.palm-touristik.com/idee.htm
Line: 55

thanks for the reply,
but this doesn't help as it's not concerning the navigation menue...