ss_perform_timeout error

This system has been running on osf5.1 for several years but started 
having ss_perform_timeout issues fairly recently. We have replaced all 
associated hardware and cables (cpu, disk cabinet, cabinet disks, power 
cords, scsi cables & controllers) except for the original boot drive but 
the problem still persists almost on daily basis. Any help to solving 
this issue is greatly appreciated.

here's the binary log event :
********************************************
Formatted Message:
    SCSI event

Event Data Items:
    Event Name        : sys.unix.binlog.hw.scsi
    Priority          : 700
    PID               : 317
    PPID              : 1
    Event Id          : 4293
    Timestamp         : 16-Jun-2006 15:37:20
    Host IP address   : 10.x.x.x
    Host Name         : hostname
    User Name         : root
    Format            : SCSI event
    Reference         : cat:evmexp.cat:300

Variable Items:
    subid_class (INT32) = 199
    subid_num (INT32) = 2
    subid_unit_num (INT32) = 152
    subid_type (INT32) = 34
    binlog_event (OPAQUE) = [OPAQUE VALUE: 1224 bytes]

============================ Translation =============================
Sequence number of error: -1452800329
Time of error entry: 16-Jun-2006 15:36:58
Host name: hostname

SCSI CAM ERROR PACKET
SCSI device class: DEC SIM
Bus Number: 2
Target number: 3
Lun Number: 0

Name of routine that logged the event: ss_perform_timeout
Event information: timeout on disconnected request

                 ############### Entry End ###############

Event information: Active CCB at time of error

                 ############### Entry End ###############

thanks,
mg