Thanks to you all, I've found the solution for my problem in the meantime. Allens hint with the .value pushed me in the right direction. I found a a post of a user with the same problem:

http://www-10.lotus.com/ldd/nd6forum.nsf/0/d2aaeebd3c340f7f852572730069702c?OpenDocument

and the solution:

"Hi there,

i had the same problem and i was very near to kill somebody...
But, in the last second, i found the solution:

The GetItemValue returns an array which seems not to be compatible with vbscript! Try this instead:

yourdoc.GetFirstItem("itemname").Text

sure, multivalue fields are not very funny, because the values are joined with ; to one string, but you will get some values back...

For me, its all i want :)"

GetFirstItem("itemname").Text works perfectly for me as well, thanks a lot to all of you taking care of my problem, this site is THE BEST source for posting such kind of problems, no doubt about it!