1) Make sure no gupdate.gcd is exist in garmin_drive:\Garmin directory.
There are 2 parts in the nuvi's sw, the boot loader and body/data
What happens is, the updater.exe will force write the bootloader to your nuvi's flash. and next, it will put the body/data in the nuvi's temporapry storage, (I think). After the nuvi boot's the new boot loader, it will READ the gupdate.gcd first, and if it not the same version with the bootloader, it will complaint the missing system software. Actually no problem the the PouchX, but, it seem to be 'tainted'

and the
ROM checking will failed at Diagnostics page..
So, I made my own 7x5TWN250 software to resolve those 2 tiny problem, without tainting any part of the software. Performance wise, both are the same.
During the process, I encountered countless "System Software Missing", but can simply undone it. So,thanks to GOD, I might be lucky this moment.