8. give yourself full USB rights

Give yourself full user rights on USB devices

Particularly using scanners can be tricky, because as a user you don't have full rights over all USB devices. A security feature, but an annoying exaggeration. Remedy this as follows:

System - Administration - Users and Groups

Click on your user name

Click on the button "Unlock"

Properties button - tab User Privileges

and make sure that every category is ticked.

Are there other user accounts but yours? Then repeat these steps for the other accounts. But, of course, for those others don't tick "Administer the system". That's a privilege that belongs only to the administrative user account (you).