I was using the HP USB scanners for more then one year. Today it refused to start, saying it cannot find any device. After reinstalling (in fact replacing) net-print/hplip the scanner worked again. I keep the system up2date, so I presume that one of the packages broke hplip without giving any warning (I did search in the elog and could not find anything). Wrote this bug just for the record. Best regards, Octavian