Core issue
The crash occurs when a vlan.dat NVRAM file is corrupt. One important step is missing in the Step-by-Step Procedure to Convert from CatOS to Cisco IOS System Software in System Software Conversion from CatOS to Cisco IOS for Catalyst 6500/6000 Switches.
Resolution
In addition to a reset of the CONFIG_FILE ROMmon variable, purge the NVRAM contents to avoid the passage of any corrupt files from Hybrid.
Issue these commands from the ROMmon privileged mode in order to purge the contents of the NVRAM:
rommon 1 > priv
rommon 2 > fill
Enter in hex the start address [0x0]: be000000
Enter in hex the test size or length in bytes [0x0]: 80000
Enter in hex the pattern to be written [0x0]: ffff
Enter the operation size 'l'ong, 'w'ord, or 'b'yte [ ]: l
rommon 3 > reset
