I dug out my old Nike+ sensor (I used to use it with a Nano) but it wouldn't connect to my 3GS. I figured the battery was dead so I bought a new one. That didn't work either. When I returned it for another one, I checked the sensor worked and would connect to my iPhone before I left the shop. I've got home and, yet again, the sensor won't connect! Anyone have any ideas as to why it won't work when I want to actually use it?