What is this mkinitramfs error message about?

[Magicloud Magiclouds <magicloud.magiclouds@gmail.com>]

Dear,
	After I compile and install 2.6.21 kernel, I run mkinitramfs like this:
/boot# mkinitramfs -o initrd.img-2.6.21 2.6.21
	While I got the error:
Error: missing mapper/rootvg-root root /dev/mapper/rootvg-root /sys entry

	This is my mount:
/boot# mount
/dev/mapper/rootvg-root on / type reiserfs (rw)
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
procbususb on /proc/bus/usb type usbfs (rw)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
/dev/sda1 on /boot type reiserfs (rw,notail)
/dev/mapper/rootvg-tmp on /tmp type reiserfs (rw)
/dev/mapper/rootvg-usr on /usr type reiserfs (rw)
/dev/mapper/rootvg-var on /var type reiserfs (rw)
/dev/mapper/rootvg-home on /home type reiserfs (rw)
/dev/mapper/rootvg-nfs on /home/nfs type reiserfs (rw)

Thanks.