Verify that all cables measure no longer than six meters total and that all SCSI connections are properly terminated. If power surges are a problem, acquire a surge suppressor or an uninterruptible power supply.
A machine's internal disk drive is usually SCSI 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 tape drives are targeted to 4 or 5, and CD drives to 6, avoiding any conflict with each other or with disk drives. If the targeting of the internal disk drive is in question, power off the machine, remove all external drives, turn on the power, and from the PROM monitor run the probe-scsi-all or probe-scsi command.
If SCSI device targeting is acceptable, memory configuration could be the problem. Ensure that high-capacity memory chips (such as 4-Mbyte SIMMs) are in lower banks, while lower-capacity memory chips (such as 1-Mbyte SIMMs) are in the upper banks.
SPARC systems do not always support third-party CD-ROM drives, and can generate a similar unknown vendor error message. Check with the CD-ROM vendor for specific configuration requirements.
Some third-party disk drives have a read-ahead cache that interferes with the Solaris device drivers. Make sure that any existing read-ahead cache facility is turned off.