Copying my bug against ubuntu-docs here, Bug #440150:
I was researching how to connect a HP 6100C scanner to Ubuntu 9.04, and encountered these docs:
ScanningHowTo
https://help.ubuntu.com/community/ScanningHowTo
Scanning
https://help.ubuntu.com/8.04/printing/C/scanning.html
Neither of these docs stated how to successfully get a scanner which SANE shows is fully supported to actually work.
I discovered this document:
Writing UDEV rules to get a SCSI scanner working on Ubuntu
http://jhansonxi.blogspot.com/2009/08/writing-udev-rules-to-get-scsi-scanner.html
which solved my problems perfectly.
I propose that something about writing UDEV rules needs to be added to the above scanning related documents. Otherwise, SANE reporting a "green check box" for compatibility is USELESS.
Also beyond UDEV rules, make sure that the scanner group has been created and the userid being logged in with is in the scanner group.