When the iPhone doesn't register the Wahoo Key it is almost always caused by dust, lint or other debris in the 30-pin connector, your phone's charging port. Syncing your iPhone only uses a few pins compared to the connector, so successful syncing and charging does not mean your connector is not contaminated. Try using canned air or a flat style tooth pick to clean the 30-pin connector. To be certain the problem is not with your iPhone, try the Wahoo Key with a different iPhone if possible.