Weird SCSI problem

Overview
Connection to SCSI Id 12 (HDD) slowly deteriorates and finally error message "Can´t save all data.............." appears.

Short description
As above.
5-6 months of use with no problem. Deterioration starts. Hard or impossible to write data to disc.
After recovering data in another PC and reconnecting the drive all seems ok for a while. Problem comes back in a few days.
No other drive is affected.
No other hw, sw or stability problems.

As soon as I reconfigure the drive to ID 14, no problem occurs. Problem seems to be hooked to ID 12..........

Hardware:
Ordinary dual Tualatin PC
1GB DDR RAM
Mobo with latest BIOS and all unused hw (Ide and so on) disabled.
Adaptec 29160, BIOS 3.10
Bunch (9) of HDD´s, all drives at default
Some other SCSI devices; no external ones
GF3TI500
3Com NIC
No OC
Win2K SP4 with adaptec latest drivers
Used as file-server.

Configuration
1. termination correct on each drive; only last at each channel
2. each drive ID's set correctly id: 0 (boot drive), id: 1, id: 2; no colliding Id´s
3. correct terminated cable being used; Ultra160 cable with active termination
4. Is the SCSI BIOS set up correctly; at defaults
5. adapter´s termination is set at aut

PLEASE GIVE ME A HINT !

I'd suspect a problem in the PCBA controller of the HDD. Have you run diagnostics on the drive in the original location and ID? Since the problem does not appear if set to 14, mechanically the drive is fine. Another possibility would be thernal conditions in that location. Does the unit have sufficient airflow to cool it?

BTW

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