I think the problem is that you are using an 80 way drive with a 50 way bus and thus only a 50 way terminator, which will not terminate all bits coming from the 80 way connector on the hard disk. You need to replace your cable with an 80 pin cable, disable termination on the controller, and add 80 pin terminators to BOTH ends of the cable.
I had exactly the same problem when I tried to use an 80 way hard drive with an 80->50 adapter and a 50 way cable. The fix I explained worked for me.
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moto