the "hw pid-prom" commands that set the correct license ID, if ran on a stack, will only apply to the master switch, there's no way to make them run on the secondary. it sounds like you ran it on the master, then imported the matching licenses on both switches? that would certainly make the second one go invalid as it no longer has a matching LID
I think you'd have to now unstack the second 6450 and wipe it, then follow the license guide on it to get the LID changed and licenses imported. then once its all valid, and your master is too, re-add it to the stack. this is why it's highly recommended to license all your stuff before stacking it
(theoretically, in a stack, you can jump to the console of secondary units by using the "rconsole 2" command, but I've tested this and it won't let you run the "hw pid" commands from that remote console)
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Also I suppose instead of unstacking it, you could also just use the other hidden method of changing the serial and LID, from the bootloader. console cable to your secondary 6450, reboot it and stop it in the u-boot bootloader, then run:
eeprom clear
eeprom sn 2ax5o2jk68e
reset
it'll reboot and let it boot fully and rejoin the stack like usual. I think you might have to reboot it twice with this method as the first boot after clearing the LID from u-boot has it re-generate one, but not take effect. second reboot has it come up fully changed. then ssh to the stack and import licenses to it, by specifying unit 2:
copy tftp license 192.168.1.8 ICX64xx/1-6450-prem.xml unit 2
copy tftp license 192.168.1.8 ICX64xx/2-6450-ports.xml unit 2
