Have you tried deleting that known connection from your X and restarting the connection process?

I had significant issues with bluetooth when I picked up my 2008 X5. I was connecting 3 phones though. The first connection worked for about 5 minutes. Spent the next 1.5 hours trying to connect another, including my CA's RAZR, trying to reconnect the original, etc. without any success.

After about the 4th restart from scratch, the first connected, then the second and then the third...