JVC GR-DVL520 Problems

Try tapping it on the side.
-only, only, only use the more expensive JVC tapes. They keep their tension far better than cheaper brands. Also, they won't rub off their oxide coatings on the heads as easily, avoiding the 'clogging' of the heads (which thereby requires constant cleaning-further damaging the heads).
-when and if you do get E- errors do a complete rewind or fast forward to the end of the tape in order to pull out tape slack. Then remove battery and tape for a while. If still screwed, then yes, sharply tap (not hard!) on the closed tape door. That may reposition those tiny switches that I mentioned earlier and get you going again.
-NEVER, EVER, EVER, leave tapes in the machine when not in use....it creates problems for the heads and the mechanisms.
-Don't leave the battery on the camera when not in use for extended periods of time. It can create problems with respect to resetting the computer controlled logic.
-there are little switches and interlocks that provide electrical feedback about the mechanical status of things to the main processor of the camera (ie. tape/no tape in camera, door open/closed etc). Over time, the mechanics get out of adjustment because of usage, humidity and certainly rough handling. So: treat the mechanisms very, very, very delicately. Don't use/store the camera in humid conditions, hot conditions or very cold conditions. Certainly don't leave it in your car---ever!
-get the camera "cleaned and ajusted" regularly to avoid these problems. (I know...more $$$$)
-I keep bags of dessicant in an insulated camera bag with the camera to maintain dryness and optimal temperatures during storage.