Hey, because I have a good day today, I did figure out what (I think) your problem is:
Look in the Backupmenu-Multiboot thread (http://talk.maemo.org/showthread.php...708#post911708).

In post #8 (http://talk.maemo.org/showpost.php?p=911708&postcount=8) it is recommended to do:

# apt-get install kernel-power-bootimg
# apt-get install --reinstall multiboot-kernel-power

You've done step 1, but (apparently) not step 2. Executing the second line should (hopefully) reconfigure multiboot.

NOW, if after that you're N900 gets a boot loop or explodes or becomes an iPhone, it's non of my business. I still recommend you read on multiboot or whatever it is you're using. Takes time but you learn a lot.