Can't boot Win 7 on second HDD from Kubuntu Trusty GRUB

[Shriramana Sharma]

Hello.

I have a system with three hard drives: 320 GB SATA, 80 GB SATA and 80
GB IDE, and in that order I have configured the BIOS boot order.

I have freshly installed Kubuntu Trusty on the 320 GB SATA disk and
Windows 7 on the 80 GB SATA disk, both on the first partitions of the
respective drives. Kubuntu shows the BIOS drives as sdb, sdc and sda
respectively, which is OK by me so long as Kubuntu works fine.

Now GRUB has no problem booting to Kubuntu. If I set the Windows disk
as the first disk in BIOS, then I have no problem booting Windows
directly either. However, when booting from GRUB I am not able to use
the Windows 7 GRUB entry created by GRUB's OS-prober, since it just
reboots the system.

As per the GRUB manual's advice regarding this issue
(https://www.gnu.org/software/grub/manual/html_node/DOS_002fWindows.html#DOS_002fWindows)
I have added the following simple entry in /etc/grub.d/40_custom (and
disabled /etc/grub.d/30_os-prober to avoid two Windows 7 entries):

menuentry 'Windows 7' {
    insmod part_msdos
    insmod ntfs
    drivemap -s (hd0) (hd1)
    chainloader (hd0)+1
}

but it says "invalid signature". If I go to the GRUB command line and
do the drivemap -s, then even afterwards, ls (hd0,msdos1) shows the
contents of the Kubuntu partition and not the Windows partition.
Perhaps this is why chainloader doesn't work? Then I tried chainloader
(hd1)+1 from the commandline, but this still reboots.

Please help.

-- 
Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा