I have inherited a server running Linux.
Every few days it pops up with this message and locks up:

ahc_pci:2:1:0: Unexpected busfree while idle
SEQADDR==0x00000018
sg[0]-Addr 0x006AD200 : Length 512
ahc_pci:2:1:0 Issued Channel A Bus Reset. 2 SCBs aborted
Recovery SCB completes
Releasing SIMQ

What does this error mean and how do I get rid of it?

It has a Adaptec SCSI Card 29160, which I replaced, but did not fix the problem.
The HD is a Fujitsu MAN3367MP.
Also attached to the SCSI card is a ARCHIVE PYTHON 04106-XXX tape drive.