emergency repair disk creation fails

I am trying to create an emergency repair disk on a windows nt 4.0 workstation (service pack 6a). When it gets to the point of formatting the disk I get the message “Setup cannot format disk” and I cannot create the disk.
I have nothing else opened, I am loggoed on as the local administrator, and this happens with whatever disk I use.
Any Ideas on what is causing this?

Thanks,
Stephen