I installed debian 5.0.4 server on a PC that has both IDE and SATA controllers.
I used an IDE HD to install the OS. The input device was a USB DVD unit.

The IDE drive showed as /dev/hda and the 4 SATA HDs showed as /dev/sda1, /dev/sda2, /dev/sda3 and /dev/sda4.

After the OS was installed the reboot started which brought up an error:
GRUB GRUB Read Error

I then disconnected the SATA HDs and rebooted successfully. So no PROBLEMS with just the IDE drive connected, grub works fine.

If I reconnect the SATA HDs though grub fails with:
GRUB GRUB Read Error

Any suggestions on the matter would be appreciated.

I have not mixed IDEs and SATAs before and maybe I should not do that, please help.

much appreciated

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I have investigated this a little further and I have concluded the following:
The problem originated when the installation got to the GRUB implementation. Here the installer engine asked me If I wanted GRUB to be installed on the MBR, to which I said YES.
The installer had listed the IDE drive (/dev/hda) before the SATA drives (/dev/sda, /dev/sdb, /dev/sdc, /dev/sdd).
After the installation finished and the machine was restarted, BIOS looked at the SATA drives first could not find the grub stages and it displayed an "Read Error".

After realising what was happening I looked at the BIOS settings to see if the HD booting sequence could be altered. The BIOS did indeed list the 4 SATA drives first and the IDE HD last. BUT it would not let me alter the booting sequence. So I was stuck with what the BIOS doing. So I decided I take the IDE drive out and create a 20G partition on the first SATA to accommodate the OS. So now everything works OK.

Thanks mys and mweed for taking the time to help me.

for info I have mixed ide and sata drives though I could only get it to work on my pc by using the sata drive followed by the IDE drive by installing to sata then adding the ide drive afterwards....

Sounds like when grub is getting hard disk info from BIOS the SATA disks are being added before the IDE drives. Grub groups all disks together in a HD#,# here the first # is the physical drive (0, 1, 2, etc) and the second is the partition (also numeric).

use the rescue mode CD for your distro. chroot to your base OS. Edit grub.conf for the new boot drive. run grub-install.