Error code #8002 isn't part of the generic GS/OS 5.0.2 operating system.
This suggests the error code is coming from the SCSI driver.
Most problems with the High Speed SCSI card come from improper
installation of the SCSI drivers. Specifically, people often don't install
the new drivers that come with the card using the original GS/OS SCSI
drivers instead.
Here are some troubleshooting steps to try:
1) Create a new boot diskette that contains GS/OS 5.0.2 and the new
SCSI drivers (the drivers are installed via the Installer program
located on the High Speed SCSI Card Utility diskette).
2) Try to copy between SCSI devices after booting with this diskette.
3) If you can copy successfully, then reinstall the GS/OS onto your
hard drive. Remember to reinstall the new SCSI drivers before
rebooting from the hard drive.
Depending on the current state of the operating system already on the hard
drive, you may have to trash the existing System and Icons folder.