Comment 20 for bug 465055

Okay, it seems to function now. It's a bit difficult to explain exactly what happened, but here is what I did:

 - Downgrade to jaunty's version of libsane
 - fix definitively permissions of device via udev (cf. infra)
 - Adjust path to firmware (strangely enough, it had changed) in /etc/sane.d/<my_scanner>.conf
 - Upgrade back to current (1.0.20-4ubuntu3) libsane version

Now it's ok.

Concerning the permissions, I created a rule in /lib/udev/rules.d/99-custom.rules:
ATTR{idVendor}=="05d8", ATTR{idProduct}=="4009", MODE="0664", GROUP="saned"
(of course, idVendor and idProduct are those given by the lsusb command and I'm member of the saned group).