why can not use chown??

["sapphire smile" <mumbojumbo_crazy@hotmail.com>]

hi,
i logged in as root,and i did below:
mount /dev/hde5 /mnt/lfs
mkdir /mnt/lfs/sources
chown lfs /mnt/lfs/sources
when i used chown command,it showed "operation not permitted"~~
why did this happen?what should i do??

/dev/hde5 fs is reiserfs~i want to build LFS in user"lfs"~~~~