Thanks Alex!
Do you think it will be a brick if i try to do the EFI modification without fixing the problem first?
This is highly of-topic for this thread, but since other people can have this in the future, I'll explain the issue.
First thing, the MP4,1 BootROM NVRAM volume is designed differently than the one from MP51 firmwares:
NVRAM volume stores: | MacPro4,1: | MacPro5,1: |
VSS: | only one | primary and secondary |
FTW: | present and works storing data about garbage collection runs. | placeholder |
Fsys: | present, stores hardware IDs and hardware descriptor | present, stores hardware IDs and hardware descriptor |
Gaid: | present | present |
The cross-flashing is a flawed process in itself since the MP4,1 NVRAM volume is designed and works differently than the MP5,1 one, the cross-flashing process does nothing about that and overtime the NVRAM volume corrupts itself and you have a brick to repair.
The warning about the secondary VSS store having a header corrupt is the first sign of a corrupted NVRAM volume.
Seems you started from one that already had issues and the cross-flashing piled upon. You gonna need to repair it before anything.