When I went to Los Angeles some time ago, I downloaded California.
However, when I got to Los Angeles, I tried to use the device, a GoLive 50, but it wouldn't switch. so I left the device on and after fifteen minutes it found itself, so to speak, then proceeded to use it the whole time I was there. On my return to the UK I did the same as you, but with no luck.
So I just set it up in the car and switched on. Again after 15 minutes it found itself back in the UK and has been fine ever since. Hope that helps.