If scanner is working for root but not for normal users then

Edit /usr/share/hal/information/20thirdparty/19-libsane.fdi
and 
add a rule for vendor and product ids. 

These Ids can be determined by using

"sane-find-scanner"

Source:
http://lists.fedoraproject.org/pipermail/users/2009-August/084540.html