Epson AcuLaser C8600 Reference Manual page 324

Invalid AUX I/F Card
This message means that the printer cannot communicate with
the installed optional interface card. Turn off the printer, remove
the card, then reinstall it.
Invalid HDD
Either the optional Hard Disk Drive is damaged or it cannot be
used with this printer. Turn off the printer and remove the Hard
Disk Drive.
Invalid IPDS
Turn off the printer and replace the IPDS module.
Invalid PS3
An optional PostScript 3 ROM module that cannot be used on this
printer is installed. Turn off the printer and remove the module.
Invalid ROM A/Invalid ROM B
The printer cannot read the installed optional ROM module. Turn
off the printer and remove the ROM module.
To clear this error, select
Reset Menu. See "How to access the control panel menus" on page
167 for instructions.
Irregular Density
If you try to print on media of overly high density, the printer
stops loading the media to prevent printer damage. In this case,
you need to clear any jammed media from the MP tray or the
paper path unit.
322 Troubleshooting
from the control panel's