"Error loading operating system" after installing Windows XP on separate partition from Windows 7

I was trying to install Windows XP on a separate partition from my Windows 7 (RC) installation, but after the first reboot of the Windows XP setup, I get "Error loading operating system" and the system halts.

Here are the exact steps I followed:

1. Installed Windows 7 on a clean drive - Windows created a 100MB system partition, then I created a 350MB partition for the O/S, and I left 125GB unallocated.
2. Installed Windows XP in a new partition allocated from 125GB unallocated space.
3. After first reboot of Windows XP setup, I get "Error loading operating system".

I attempted to fix the problem using the "Startup Repair" tool on the Windows 7 installation DVD, and although it found a "master boot record corruption" and fixed it, I still get the same error after rebooting.

Solution 1:

Windows 7 would have to be the last OS installed. The XP bootloader may be unable to handle Windows 7, but the other way around is likely fine. Try fixing your mbr (/fixmbr) from a Win 7 recovery console.

Solution 2:

I can confirm that the XP bootloader does not handle Windows 7 well, and that even reinstalling XP over a HD that previously had windows 7 on it can be a hairy experience.

Standard practice for multibooting Windows is to install OS versions in order from oldest to newest, and so far as I am aware this may even be a MS recommendation, with other install orders being unsupported.

I would recommend to blow away both OSs and start from scratch again in the correct order (i.e. XP first).