On any model other than D followed by two digit models this problem is caused in 90% of cases by the mechanism not returning to its fully stopped position properly after carrying out and operation, thereby not activating the appropriate sensor. The thumping operation jolts the mechanism into the proper position whereby the sensor can send the signal to the mechanism that all is normal, as beforehand the logic circuits acted as though the mechanism had jammed whilst conducting various operations, like loading or unloading etc. Sometimes (only sometimes) even just pressing slightly on the cassette door can correct the fault.

E-04 of course is a warning on any JVC camcorder that there is a problem with data transfer between the video drum and the associated circuitry, but its suspected that this could be a rogue warning. (a false warning)

Ant I take it that your connections can offer accomodation in Turkey at a price?

I have the same experience with my camera. It has been in repair but that didn't help. What you can do is hit the camera a little but unpleasant on the side and the error message E04 will disappear for the time the camera is switched on. The error message can (or better will) possibly come back, but now you know what to do.