INIT: no more processes left in this runlevel

[unix syzadmin]

Hi,

This is a RHEL4 U1 server.  We are unable to restart this server using "init
6" or "shutdown -r now" command.

---------*******---------
# more /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant Update 1)

# who -r
         run-level 3  Aug  3 02:43                   last=S

# uname -a
Linux lnx101 2.6.9-11.ELsmp #1 SMP Fri May 20 18:26:27 EDT 2005 i686 i686
i386 GNU/Linux
---------*******---------

At the console it gives the below messages and seems to be hung.

---------*******---------
Unmounting pipe filesystems
Unmounting filesystems:
umount2: Device or resoruce busy
umount: /usr device is busy
umount2: Device or resource busy
umount: /usr device is busy

INIT: no more processes left in this runlevel [failed]

---------*******---------
Please suggest
Thanks.