the c6msfc3 doesn't seem to have a boot image for disaster recovery :(
I got into that mess one day. I tried booting using the device name of "disk0:", and "sup-disk0:" with no success. What I did was to boot the switch up using the Native IOS image.
Before I did this, I changed the config register on the MSFC3 to 0x2102, using the "confreg 0x2102" command. When the sup booted its piece of the Native IOS image, the MSFC3 automatically booted up its piece of the native ios code. From there I was able to copy the Hybrid MSFC3 image to the MSFC3 bootflash, and converted the switch back to hybrid mode.
