As RoHe suggested, I went to the Setup Utility, turned off the empty terminals, and made sure all of the active terminals were turned on (mine already were, and all the drives were already working). Brief instructions follow, if anyone else is having the same problem and is feeling brave about doing it themselves:
**in the Setup Menu, to go [Drives] (initially not expanded; strike "enter" to expand the group)
**scroll through the drives and look at the details for each drive (0-5 on my computer):
--any full port will give details about the drive attached, and should be [On] (hit enter to get to the on/off toggle)
--any empty port will have "Controller details" but no "Drive details", and should be [Off] to avoid this problem at startup.
--that did it for me! (I had to turn 1 and 3 off)
Happy debugging! I hope this helps someone!