VC-1-SH: Troubleshooting / Check Settings
Make sure that the mode switches are matching those of the units that are working and test them with the same signals in/out that you are using with the three that are working. Let me know if you still have problems after verifying that the mode switches are matching and sources too.
Are you using the software to change the settings for the units? it's possible that you may need to take a look at the settings through the software to make sure they're matching.
Go here to download the remote control software and install it and check the settings. Also if the unit is not up to date you can update the firmware.