I've had this "can't find your vehicle right now problem" for the last six months or so, possibly starting after the 3.1 upgrade. The turn-by-turn directions did work fine for the first few months with 3.0 though. The system first worked and then stopped working with a Motorola Razr2 V9 on AT&T. Thinking it might be a phone issue, I switched to a Verizon Blackberry Tour (switching my active number on the sync website). Since the same problem occurs for me with two different phones on two carriers, it may suggest this is a Sync problem not a phone or carrier problem. I tried the suggestions in this thread and given to me by the Sync phone support team, including turning up the bluetooth volume, performing a master reset, deleting my saved points, and pulling my phone battery to "clear possible bluetooth errors". However the result is the same - "I'm sorry, but I can't find your vehicle right now".
I also have a second problem with Services, that I think started along with the turn by turn issue. When I do a business search, and then have Sync dial the business number for me, the phone over Sync just rings and rings, like the business never picks up. However, if I immediately call the business directly, or using another phone, the business does pick up. So it seems like the Sync-dialed number is not really calling the business. This used to work for me, too, with the Razr2/AT&T.
Looking forward to reading about a solution!