Troubles with multipath configuration

Hi all,
i have some problems configuring my multipath daemon on Debian Etch. The system periodically reports that a path is going down, and some seconds after the path come back active. I'm using two server IBM linked to an IBM TYotal storage via fiber channel HBA. Every server has two HBA (that's the reason i'm using multipath).

The errors in the syslog are like:

Aug 7 08:15:23 rpiemdeb1 multipathd: sdb: readsector0 checker reports path is down
Aug 7 08:15:23 rpiemdeb1 multipathd: checker failed path 8:16 in map mpath0
Aug 7 08:15:23 rpiemdeb1 kernel: device-mapper: multipath: Failing path 8:16.
Aug 7 08:15:24 rpiemdeb1 multipathd: mpath0: remaining active paths: 1
Aug 7 08:15:24 rpiemdeb1 multipathd: sdd: readsector0 checker reports path is down
Aug 7 08:15:24 rpiemdeb1 multipathd: checker failed path 8:48 in map mpath0
Aug 7 08:15:24 rpiemdeb1 multipathd: mpath0: Entering recovery mode: max_retries=10
Aug 7 08:15:24 rpiemdeb1 multipathd: mpath0: remaining active paths: 0
Aug 7 08:15:24 rpiemdeb1 kernel: device-mapper: multipath: Failing path 8:48.
Aug 7 08:15:28 rpiemdeb1 multipathd: mpath0: Entering recovery mode: max_retries=10
Aug 7 08:15:28 rpiemdeb1 multipathd: mpath0: Entering recovery mode: max_retries=10
Aug 7 08:16:00 rpiemdeb1 multipathd: sdb: readsector0 checker reports path is up
Aug 7 08:16:00 rpiemdeb1 multipathd: 8:16: reinstated
Aug 7 08:16:00 rpiemdeb1 multipathd: mpath0: queue_if_no_path enabled
Aug 7 08:16:00 rpiemdeb1 multipathd: mpath0: Recovered to normal mode
Aug 7 08:16:00 rpiemdeb1 multipathd: mpath0: remaining active paths: 1
Aug 7 08:16:04 rpiemdeb1 multipathd: sdd: readsector0 checker reports path is up
Aug 7 08:16:04 rpiemdeb1 multipathd: 8:48: reinstated
Aug 7 08:16:04 rpiemdeb1 multipathd: mpath0: remaining active paths: 2
Aug 7 08:35:00 rpiemdeb1 multipathd: sdb: readsector0 checker reports path is down
Aug 7 08:35:00 rpiemdeb1 multipathd: checker failed path 8:16 in map mpath0
Aug 7 08:35:00 rpiemdeb1 kernel: device-mapper: multipath: Failing path 8:16.
Aug 7 08:35:01 rpiemdeb1 kernel: device-mapper: multipath: Failing path 8:48.
Aug 7 08:35:01 rpiemdeb1 multipathd: mpath0: remaining active paths: 1
Aug 7 08:35:01 rpiemdeb1 multipathd: sdd: readsector0 checker reports path is down
Aug 7 08:35:01 rpiemdeb1 multipathd: checker failed path 8:48 in map mpath0
Aug 7 08:35:01 rpiemdeb1 multipathd: mpath0: Entering recovery mode: max_retries=10
Aug 7 08:35:01 rpiemdeb1 multipathd: mpath0: remaining active paths: 0
Aug 7 08:35:07 rpiemdeb1 multipathd: mpath0: Entering recovery mode: max_retries=10
Aug 7 08:35:07 rpiemdeb1 multipathd: mpath0: Entering recovery mode: max_retries=10

And here's my mutipath.conf:

defaults {
udev_dir /dev
polling_interval 30
selector "round-robin 0"
path_grouping_policy failover
getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
prio_callout /bin/true
path_checker readsector0
rr_min_io 1000
rr_weight uniform
failback 10
no_path_retry 10
user_friendly_names yes

}

blacklist {
devnode sda
}

multipaths {
multipath {
wwid 3600a0b8000199d0a00003f6646b03b5f
}
multipath {
wwid 3600a0b8000199eff000003da46b03ab4
}
}

devices {
device {
vendor "IBM"
product "DS4300"
}
device {
vendor "IBM"
product "D4300"
}
}

Probably some wrong configuration?

Thanks