skanlite, simple scan
there is other two but can't remember names
i was mistaking a 3300 with a 640p, the one we tested, i had a mess with a 3300 but hp, sorry, i haven't used your particular model
it would be useful to reinstall xsane just to discard possible errors in packages, be sure to have your system fully updated, open synaptic and press reload, apply all updates and then reinstall xsane
i was reading this page
http://www.sane-project.org/sane-mfgs.htmlit says that your benq 3300U(because acer was part of benq that time, still is maybe) is in good support condition on the xsane 1.0.22 and we have that version, with 3 fixes over it, sane seem to be breaking alot lately, my scanner is supported by sane but it doesn't work, i could find unofficial(something not recommended in pclinux, but sometimes you need to do this) drivers for it and it is working perfectly
it mentions version of the backend 1.4 in the xsane version it seems that we have it