Sorry guys but no success.
What I did:
1. Format my Nuvi
2. Copy my backup files from PC to Nuvi
3. Start Nuvi - it works, but the GarminDevice.xml has strange symbols at the end (as I wrote befor)
4. Place the Gupdate.gcd file with alternative SG firmware into System folder of Nuvi
5. Turn on the Nuvi and it start to flash. Flashed good, so I could test it with alternative SG firmware. It works and GarminDevice.xml is look good.
6. Place the Gupdate.gcd file with original EU 5.10 firmware into System folder of Nuvi
7. Turn on the Nuvi , it start to flash. Flashed good. Everything works but GarminDevice.xml has strange symbols at the end again.

I have tried to use another original firmwares (3.90 - 5.40) but obtain the same corrupt GarminDevice.xml file.