What ID is the HD set to? Check it is NOT set to 7 (the Supra controller is /probably/ set to that.
Assuming you only have the hard disk on the controller, check that the drive itself is terminated, and remove the external terminator. Ensure that the controller is supplying term power. If the docs do not state that it does, set the TERMPWR jumper on the drive. If both controller and drive are supplying term power, this shouldnt be a problem.
ISTR the Supra uses a 25pin external "SCSI" connector. This is an abortion of a connector, and is non-standard: for example, it ties most of the ground pins together... allegedly.
Check the controller itself is terminated. This is NOT the external terminator on the rear port, but should be inside the case itself. A SCSI bus must be terminated at each end.
Check cabling is fully inserted into the sockets on both the controller, and the drive. Have a good gander at the cable, and check for any damage, check sockets for bent pins, and reseat cable.
On the Amiga, double check the spelling of the device driver in device= in the supra software .info file, and check this matches the device driver in Devs:
Hard boot, and post results; eliminate potential issues from the wire up.
