2.50 service firmware gives GIR version mismatch error - that was first service firmware which i have tried. I fully agree - such behavior looks very bad :D Garmin already contacted, i'm waiting for response. Damn, what a sensitive unit - with 205 i don't have such problems..

P.S. With service firmware it freezes on loading maps only when not connected to PC. If i plug it into USB, it normally shows connection icon, but can't be recognized by PC.

Problem solved without Garmin costly help

Steps:

1. Load cure firmware as usual
2. switch on Nuvi, and tap left top corner, but after 0.5 - 1 secs later, than for pre-boot mode
3. wait for "Loading maps", then wait 5-7 secs and press power button
4. wait for copyright sign (C) and release power button
5. wait for language selector and release top left corner
6. IMMEDIATELY and very fast tap few times Ok button
7. Enjoy Nuvi
8. connect to PC, erase bad files and restart.

Many thanks to RTuERkaM from gps-forum Russia for its support and persistence.

P.S. You must experimentally select time in step 3. If selected time will be to short you don't see (C) - Nuvi will be switched Off.

New thing, related to my finding:
even with cure firmware my unit do not recognized by PC. More, when i found this workaround, unit not connected to PC, behavior was exactly same as after unsuccessful maps upgrade. So, if anyone has Nuvi, which needs to be cured, lets try my method WITHOUT cure firmware. And please report results here