Core issue
A software upgrade on the active Supervisor fails even after you copy the code from the bootflash on the secondary (up and running new code) directly to the bootflash on the primary.
Cisco IOS on both Supervisor Engines must be the same for them to operate properly. When the active Supervisor downloads its configuration to the standby, it copies its own boot variable to the standby. If the standby Supervisor does not have the same image as the active Supervisor, it becomes stuck on a boot loop because it is not able to find the image.
Resolution
Remove the active Supervisor, get into ROMmon on the Supervisor that does not boot and boot it up manually, because it is trying to load the same image that is in the other Supervisor Engine. Reset your boot variables once the IOS is loaded.
After you recover the first, and original, Supervisor Engine, you need to upgrade one of the Supervisor Engines in order to have the same image.
