Need some help and assistance here. I recently changed my kit lens to a Tamron 18-200 mm F/3.5 - 6.3. The first day I was using it, it was perfectly fine. After taking around 50 photos, the autofocus function of the 300D wouldnt function anymore. It just keeps focusing and unfocusing, but wouldnt really focus properly. Still managed to get good and clear shots with the Manual focusing. Tried to change back to the kit lens and 50 mm prime lens, but the same problem persisted. Any idea whats wrong?