Hello everybody
I've donwloaded the newest version of SWFUpload (Version 2) from http://www.swfupload.org/node/1/release and replaced the file
jsparty/SWFUpload/SWFUpload.swf
with this one
swfupload/FlashDevelop/Flash9/swfupload_f9.swf
from the archive
And now, it works on my server.
It would be nice if somebody could try this on his website and post here, if this works for him, too.
PS: Don't forget to clear the cache...
phinel