i found the problem to error code o4. the problem is there is a very thin spring thats mount just above the camcorder recording head. if thats bent, this will not let tape eject. no matter what u do. so you miht to left up the VHS-C tape head cover up to see the little spring.

I'm assuming your E04 code is on a JVC product. I too have suffered with this problem and you have to options pitch it or give it a good whack on the side with your hand. Make sure the tape door closed (no tape loaded. This works for me every time.