Comment 8 for bug 537849

I have got the same problem.
HP ProLiant ML110 G6 with Lights-Out card. Ubuntu 10 LTS.
The card offers an independent system providing access over network (separate Ethernet interface) to serial interface (COM1).
I could setup BIOS access quite easily. I had no problems to provide login prompt and terminal access to the system.
The only issue was with GRUB and messages as stated above.
As far as I understand what is happening:
 - BIOS grabs the serial interface to provide console services there.
 - As the control is passed to grub the ttyS0 is still grabbed by BIOS service.
 - GRUB tries to setup the port with "serial" command and it causes "error: bad unit number." message.
With that observation I simply decided to "use" this redirection, so I let GRUB use the "console".
GRUB thinks he is writing on the screen, but BIOS redirects this output to ttyS0 (COM1).
Here is my config:
===============
GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT=7
GRUB_HIDDEN_TIMEOUT_QUIET=false
GRUB_TIMEOUT=7
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet"
#GRUB_CMDLINE_LINUX=""
GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8"

# Uncomment to disable graphical terminal (grub-pc only)
GRUB_TERMINAL=console
#GRUB_TERMINAL=serial
#GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
===============
The only disadvantage is "jumping cursor" (it appears like crazy in various positions on the screen).
Apart of that you have 7 seconds to press ESC key to stop autoboot. If you press the key the GRUB menu appears.
So now I have remote access to all three stages - BIOS setting, GRUB menu and system console.