Input/output error on files on a lvm snapshot

Occasionaly I get _LOTS_ of this kind of errors from a LVM snapshot i have mounted.

dmesg gives these 2 interesting lines:
--------------------------------------
EXT3-fs error (device lvm(58,4)): ext3_readdir: bad entry in directory #1327138: rec_len % 4 != 0 - offset=0, inode=1922062006, rec_len=43729, name_len=218
EXT3-fs error (device lvm(58,4)): ext3_readdir: bad entry in directory #1376515: rec_len % 4 != 0 - offset=0, inode=2932214113, rec_len=4999, name_len=53

which fits perfectly well with the snapshot:
--------------------------------------------
brw-rw---- 1 root disk 58, 4 Oct 27 07:00
week_snapshot_opt_1035698402

which is mounted:
-----------------
/dev/optVG/week_snapshot_opt_1035698402 on /snapshots/opt/week type ext3 (ro)

lvdisplay:
-----------------------------------------------------------------------------

ve:/sbin# lvdisplay /dev/optVG/week_snapshot_opt_1035698402 
--- Logical volume ---
LV Name                /dev/optVG/week_snapshot_opt_1035698402
VG Name                optVG
LV Write Access        read only
LV snapshot status     active destination for /dev/optVG/opt
LV Status              available
LV #                   5
# open                 1
LV Size                40 GB
Current LE             2560
Allocated LE           2560
snapshot chunk size    64 KB
Allocated to snapshot  57.44% [1.14 GB/1.99 GB]
Allocated to COW-table 8 MB
Allocation             next free
Read ahead sectors     1024
Block device           58:4

lvdisplay of the real LV:
------------------------------------------------------------------------------

ve:/sbin# lvdisplay /dev/optVG/opt 
--- Logical volume ---
LV Name                /dev/optVG/opt
VG Name                optVG
LV Write Access        read/write
LV snapshot status     source of
                       /dev/optVG/week_snapshot_opt_1035698402 [active]
                       /dev/optVG/1hour_snapshot_opt_1036062001 [active]
                       /dev/optVG/8hours_snapshot_opt_1036047601
[active]
                       /dev/optVG/day_snapshot_opt_1036018801 [active]
LV Status              available
LV #                   3
# open                 1
LV Size                40 GB
Current LE             2560
Allocated LE           2560
Allocation             next free
Read ahead sectors     1024
Block device           58:2

The strange part is that some files works, and some doesnt ?? Is this a snapshot error, a filesystem error, or combinations ? I run EXT3 on all my filesystems, and i only see the problem on snapshots. They are read only though, so it could be that EXT3 doesnt like read-only. Has anyone experienced anything like this?

JonB