It keeps ejecting the disc and saying disc error

Now what this joker isn't telling you is that the 'hack' below actually resets the player to factory defaults. It just worked for me perfectly.

Now you might have to go back into setup and readjust some of your settings. (i.e. freq response)

1. press SETUP on the remote
2. Go to "TV Aspect" and move the cursor to "16:9"
3. Press in order: 1, 3, 9, 7, 1, 3, 9 on the remote, then press ENTER

1. Power up unit with no disk in the tray
2. After "no disc" shows on the front display, press PAUSE on the remote
3. Press in order: 1, 4, 7, 2 on the remote (short keypresses). A new screen will show up, EEPROM settings with a green background
4. Write down the EEPROM string for backup/restore purposes in case you screw up. My string was 55 53 00 45 02 55 64 FF (compare with the default string of the 312, which is 55 53 00 45 14 55 64 FF).
5. To enable VCD playback, move the cursor to the "45" (4th group of characters from the left; use the remote up/down arrows to move right/left) and enter "46" or "47" instead, then press ENTER to commit
6. To enable SVCD playback, move the cursor to the "64" field (second from the right) and enter "FE" instead. To enter "F" press "6" on the remote and keep pressed. To enter "E" press "5" on the remote and keep pressed. After you're finished entering "FE" press ENTER on the remote to commit
7. Press PAUSE on the remote to exit the EEPROM screen
8. Power off, then power on again the player
9. It now plays SVCDs and/or VCDs depending on the codes you entered.

The final EEPROM strings with both VCD and SVCD enabled are:
55 53 00 46 02 55 FE FF and
55 53 00 47 02 55 FE FF
(either works)

NB the replacement of 64 by FE was in the past wrongly labeled as Macrovision hack. That's not true. What it really does is enable SVCD playback. If you only do the #5 above, you'll only get VCD playback. If you only do the #6 above, you'll only get SVCD playback. If you do both, you'll get VCD and SVCD playback.

(SVCD playback was especially important to me because I have several hundreds of them - mostly TV shows recorded on my TiVo, then exported to the PC and converted to SVCD)

The other hack for the DVB-312 also works on the 412 (see the configuration screen):
1. press SETUP on the remote
2. Go to "TV Aspect" and move the cursor to "16:9"
3. Press in order: 1, 3, 9, 7, 1, 3, 9 on the remote, then press ENTER

The info showing on that screen for the DVB-412 is:

Model: Zenith ZV8020001
Region: 1
Chip ID: M3355A-B
Servo ver: S101_43180
Microcom ver: V1.50A MP
PROM: 55 53 00 45 02 55 64 FF
Factory reset... done...
(the PROM I listed above is before the VCD/SVCD hack)