virtualbox.org

I am running a Windows 7 host and many Windows 7 guests.
One of these needed to run the windows repair disc.
I put it in the host drive and selected that from the devices dropdown.
I then restarted the VM and select to boot from the CD. Error resulted
Non-system disc or corrupted disc.
What am I doing wrong?

Please quote error messages precisely.

If the message told you that the disk is not bootable, then it's not bootable - i.e. it contains no boot code.

I would guess that the repair disk is meant to be run from windows, not used to boot the PC.

Also, many "system repair" CDs work in conjunction with a hidden partition on the PC the CD was bundled with. The partition contains the actual working code. Obviously that partition doesn't exist in a VM.

I think I understand.
The disc in question was created on a system which uses UEFI. This might mean that it is only useful on the same system or a similar one. I had checked that the disc was bootable in the machine I created it on so I know that bit was OK. However the UEFI is probably the cause.
Now that I have solved the other problem of writing to a CD on the machine I think it should work.
Its these little things that jump up and say GOTCHA!
Again it GOTME having created the repair disc apparently successfully I tried to boot from it and got an error
FATAL: Could not read from the boot medium! System halted.

Now what??

Please see my previous answer. As far as I can tell you have changed nothing of relevance.

Btw. I don't claim to be an expert, but I don't see how having a UEFI host could change how a bootable data CD/DVD is formatted. If that was the case we would need different CD standards for EFI and non-EFI PCs - and I don't recall retail install packages being marked with anything like that.

Your original post gave no hint that you were authoring the disk yourself. How exactly are you doing it? I hope you are aware that copying a bunch of files to a CD does not create a bootable installer?

No not self authored.
Backup/Restore>Create a Repair disc on the VM in question.
Now I can write to the CD it creates the disc.
Restart the VM, F12 select option c the option for the CD drive, and get the Error?