E-O4 is an indication that there is a problem of data transfer between the video drum and its associated circuitry and can appear for something as simple a dirty video head, however if this does not apply then the head itself could be defective or the ribbon cable that connects it. Another reason can occasionally be that the mechanism has not returned to its correct stop position after having carried out an operation (load / unload etc) thereby not activating a position sensor, and its in these cases that some people find that lightly thumping (with hand) the bottom of the camcorder can correct the fault, or alternatively sometimes by pressing lightly on the cassette door. Unfortunately the latter reason (should it apply!) is an extremely a common one which to be quite frank about it there is no permanent easy cure for, as basically its more of a mechanical construction problem.