Also, check cable connections and make sure that the SCSI termination is proper. Remember that only the last device on each end of the adapter card should be terminated. If you are unsure that the termination is set correctly, consult your owner's manual. Termination is set different ways on different recorders and other SCSi devices. Some use jumpers, some use removable terminating resistors.
External drives use a plug in terminator on outside of the external case.
Make sure that any external devices are not terminated on the device itself. Remember that SCSI cable length is limited to 19.6 feet, including all internal cabling. If the setting is correct, and you are still having problems, switch the master and slave drives and reset the jumpers accordingly. IDE transfer rates are traditionally slower that SCSI, so buffer underruns are more likely on IDE drives. Although it takes extra time, it is usually a good idea to do a burn in test mode before initiating the actual recording.