This message always appears at the beginning of rebooting. If there is a problem, the system hangs, and no other messages appear. This condition is caused by conflicting SCSI targets for the boot device, which is almost always target 3.
The boot device is usually the machine's internal disk drive, target 3. Make sure that external and secondary disk drives are targeted to 1, 2, or 0, and do not conflict with each other. Also make sure that the tape drives are targeted to 4 or 5, and CD drives to 6, avoiding any conflict with each other or with the disk drives. You can set a device's target number using push-button switches or a dial on the back near the SCSI cables. If the targeting of the internal disk drive is in question, check it by powering off the machine, removing all external drives, turning the power on, and running the probe-scsi-all or probe-scsi command from the PROM monitor.