Take anything either say with a grain of salt. Long SCSI cables are often troublemakers. The tiny internal wires can fray, jacks can become damaged, and shielding can rupture. Generally, the thicker and heavier the cable insulation and sheilding, and the more robust the connectors, the more reliable a SCSI cable will be. If you're having problems try changing the order of SCSI devices in the chain.
Scanners often like to be the first device in the chain.
Keep SCSI Probe, an invaluable little freeware utility, on your hard drive. SCSI Probe helps you mount stubborn SCSI devices,and can help sleuth what the trouble is if they won't mount. Sleep mode is not good enough here. Your PowerBook needs to be shut down. Do not unmount a PowerBook's SCSI icon by dragging it to the Trash.