SCSI error, where to look?

[Per olof Ljungmark]

Adaptec 2940UW with Compaq branded Quantum Atlas, about a year old. 
Cable is new. Erros are coming more and more frequently so I guess it's 
the drive?

Is it possible from the following information to decide where to start 
looking for the problem:

  kernel: (da0:ahc0:0:0:0): parity error detected in Message-in phase. 
SEQADDR(0x9b) SCSIRATE(0x87)

TIA