instalation problem - unable to find device node

[javo]

hi ,
I'm newbie to FreeBSD, I tried to install it month ago and everything was
OK, freeBSD was the only system running,

later, I've installed windows and gentoo, and I've left space for FreBSD,
now during the instalation I got this error after configuring my disk
partitions,

unable to find device node for /dev/x in /dev! and instalation won't
continue

what can be the reason pls? thx