Hi,

Something similar is also happening to me on Dapper LTS 6.06.2 with Kernel 2.6.15-52-amd64-server.

I do not have a way of reproducing this at will.  

In summary, I have the primary volume (u01) of 450GB sitting in a VG using a PV on /dev/cciss_c0d1p1, so no mdraid or other layering. Creating a 15GB snapshot of of the volume works as expected. 

# lvcreate -s -n test1 -L 15G vg01/u01
  Logical volume "test1" created
#

I can then mount and use the snapshot.

Creating a second snapshot of the volume then resulted in:
# lvcreate -s -n test2 -L 20G vg01/u01
  Logical volume "test2" created
#

However, the volume is not usable:
# lvdisplay vg01
  --- Logical volume ---
  LV Name                /dev/vg01/u01
  VG Name                vg01
  LV UUID                Be69s5-zvtC-OKp3-IJDR-MQFe-YWPe-A7Bm1S
  LV Write Access        read/write
  LV snapshot status     source of
                         /dev/vg01/test1 [active]
                         /dev/vg01/test2 [INACTIVE]
  LV Status              available
  # open                 1
  LV Size                450.00 GB
  Current LE             14400
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           254:3

  --- Logical volume ---
  LV Name                /dev/vg01/test1
  VG Name                vg01
  LV UUID                PYhpfX-5Wl3-x487-h4x6-Gb2y-7N1j-x4XB2c
  LV Write Access        read/write
  LV snapshot status     active destination for /dev/vg01/u01
  LV Status              available
  # open                 1
  LV Size                450.00 GB
  Current LE             14400
  COW-table size         15.00 GB
  COW-table LE           480
  Allocated to snapshot  0.40%
  Snapshot chunk size    8.00 KB
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           254:12

  --- Logical volume ---
  LV Name                /dev/vg01/test2
  VG Name                vg01
  LV UUID                HKyqse-NSu3-5b2y-So54-xZsr-oiNK-ndExdP
  LV Write Access        read/write
  LV snapshot status     INACTIVE destination for /dev/vg01/u01
  LV Status              available
  # open                 0
  LV Size                450.00 GB
  Current LE             14400
  COW-table size         20.00 GB
  COW-table LE           640
  Snapshot chunk size    8.00 KB
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           254:14

#

And I see these errors in dmesg:
[792276.624583] attempt to access beyond end of device
[792276.624591] dm-13: rw=17, want=569894688, limit=41943040
[792276.624596] device-mapper: Error reading/writing snapshot
[792276.665813] attempt to access beyond end of device
[792276.665819] dm-13: rw=17, want=569902896, limit=41943040
[792276.923219] attempt to access beyond end of device
[792276.923225] dm-13: rw=17, want=569894688, limit=41943040
[792276.965357] attempt to access beyond end of device
[792276.965362] dm-13: rw=17, want=569902896, limit=41943040
[792277.253731] attempt to access beyond end of device
[792277.253737] dm-13: rw=17, want=569894688, limit=41943040
[792277.805186] device-mapper: snapshot is marked invalid
root@uxlon07:~#

It seems that most times when I do the following:
* create snapshot snap1
* use snapshot snap1
*create snapshot snap2

then snap2 is invalid, but if I dont use snap1 then things seem to be ok.

Regards,
Mike