Panasonic video cassette recorder NV-HD660B
F04 Error message
Tried switching off at the mains and on ( with holding the power on button in and also not).
Before getting too involved with the F04 error code which relates to loading/unloading, try turning the vcr upside down, give it a good shake and a couple of light taps, and while the unit is still upside down, press eject. This will work in many cases. If your machine has a front panel which folds down then obviously lift that up before pressing eject!
Good luck!