I've had no problems with lock-ups on my 168 with 5.1 or 5.21. It may be best to do a factory re-set and start from scratch. If you get the faster card and use a Card Reader, the maps are installed much quicker.
I checked the Mio site and found the 168 will take a faster card x133 (actually about 20MB read/write) so I purchased a
Kingston 512MB SD Ultimate x133 and it has got rid of the lag and the late final turn left/right instruction. Check here >
http://www.choicestationery.com/acat...d_Digital.html