after 11.04 upgrade SOME usb device doesn't automount

I have several usb device that I plug/un-plug on a regular base.
All of them were working fine and could auto-mount until upgrade 10.10-->11.04
Before, when I connected an usb device, a dialog asking what to do with the new plugged device was popping out and I could "safely remove drive" by right clicking on the icon in nautilus)
Now, one of my mp3 player (lenco xemio touch) is not auto-mounted when connected and I can't access to the files (my external usb hd and another mp3 player are working fine)
I have made the 11.04 upgrade, then (for other reasons) I have made also a fresh install of 11.04: In both cases the problem was persisting.
I have tried several solution (installing/un-installing usbmount, mountmanager, halvt (script install problem),...) but none of them was working

lsusb: (I think it doesn't show my mp3)
Bus 008 Device 004: ID 413c:2010 Dell Computer Corp.
Bus 008 Device 003: ID 413c:3016 Dell Computer Corp. Optical 5-Button Wheel Mouse
Bus 008 Device 002: ID 413c:1003 Dell Computer Corp. Keyboard Hub
Bus 008 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 005: ID 046d:c719 Logitech, Inc.
Bus 006 Device 004: ID 046d:c718 Logitech, Inc.
Bus 006 Device 003: ID 413c:8130 Dell Computer Corp.
Bus 006 Device 002: ID 046d:0b05 Logitech, Inc.
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 003: ID 0644:0201 TEAC Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID beef:0006
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

fdisk -l: show nothing (empty???)
/etc/fstab is empty??? (I can't understand how it is possible=>I have 2 disk raid)

after an un-plug and a plug of my problematic mp3, dmesg is giving that:
[ 5959.780045] usb 1-1: USB disconnect, address 5
[ 5977.605106] usb 1-3: USB disconnect, address 4
[ 5977.860026] usb 1-3: new high speed USB device using ehci_hcd and address 6
[ 5977.928204] hub 1-0:1.0: unable to enumerate USB device on port 3
[ 6023.224023] usb 1-3: new high speed USB device using ehci_hcd and address 7
[ 6023.356340] usb 1-3: config 1 interface 0 altsetting 0 bulk endpoint 0x81 has invalid maxpacket 256
[ 6023.356345] usb 1-3: config 1 interface 0 altsetting 0 bulk endpoint 0x1 has invalid maxpacket 256
[ 6023.357792] usb-storage 1-3:1.0: Quirks match for vid 071b pid 3203: 400
[ 6023.357837] scsi10 : usb-storage 1-3:1.0
[ 6024.356629] scsi 10:0:0:0: Direct-Access ARCHOS 1 Vision Player 1.11 PQ: 0 ANSI: 0
[ 6024.357434] sd 10:0:0:0: Attached scsi generic sg7 type 0
[ 6024.358720] sd 10:0:0:0: [sdg] 7856128 512-byte logical blocks: (4.02 GB/3.74 GiB)
[ 6024.360857] sd 10:0:0:0: [sdg] Write Protect is off
[ 6024.360861] sd 10:0:0:0: [sdg] Mode Sense: 03 00 00 00
[ 6024.361595] sd 10:0:0:0: [sdg] No Caching mode page present
[ 6024.361600] sd 10:0:0:0: [sdg] Assuming drive cache: write through
[ 6024.364223] sd 10:0:0:0: [sdg] No Caching mode page present
[ 6024.364228] sd 10:0:0:0: [sdg] Assuming drive cache: write through
[ 6024.365420] sdg:
[ 6024.367602] sd 10:0:0:0: [sdg] No Caching mode page present
[ 6024.367605] sd 10:0:0:0: [sdg] Assuming drive cache: write through
[ 6024.367608] sd 10:0:0:0: [sdg] Attached SCSI removable disk
[ 6075.566751] usb 1-3: USB disconnect, address 7

Any idea?
Thanks,
Baudouin