I googled around a bit and have a couple of things you might try. First, in XSane preferences, disable the "Enable Color Management" option.
Second, can you scan correctly by opening the GIMP (Applications>Graphics menu) and going to File->Acquire->Xsane->Device Dialog?
Also, it may help, if you haven't already done so, to install all of the sane backend stuff (by default it's not all there). Run:
After that, restart the machine and see if anything changes.
sudo apt-get install sane
Installing the whole sane package will also add a third image-scanner program called xscanimage (you will have to call it from the command-line) that might give you better luck. Probably not, but it's worth a shot.
Please let me know if any of this stuff helps.