Hi
It may be that the CK-7W memory is full. With the car off, push and hold the control button for 10 seconds until you hear a beep and this will wipe the memory.
Please note that his car kit was replaced just over two years ago with the CK-100, as it has no echo / noise cancellation and cannot be updated with new software (the CK-100 has this feature) so you may have issues with compatibility or echo on some handsets.