diff -up ./examples/hocr-gtk/sane-pygtk.orig ./examples/hocr-gtk/sane-pygtk
--- ./examples/hocr-gtk/sane-pygtk.orig	2010-06-07 01:21:33.000000000 +0300
+++ ./examples/hocr-gtk/sane-pygtk	2010-06-07 01:23:06.000000000 +0300
@@ -39,14 +39,14 @@ comments = "SANE (Scanner Access Now Eas
 
 # set gettext support
 locale_dir = '/usr/share/locale'
-try:
-    import locale
-    import gettext
-    locale.setlocale(locale.LC_ALL, "")
-    gtk.glade.bindtextdomain(app_name, locale_dir)
-    gettext.install(app_name, locale_dir, unicode=1)
+try:
+    import locale
+    import gettext
+    locale.setlocale(locale.LC_ALL, "")
+    gtk.glade.bindtextdomain(app_name, locale_dir)
+    gettext.install(app_name, locale_dir, unicode=1)
 except (IOError,locale.Error), e:
-    print "WARNING: Can't load locale"
+    print "WARNING: Can't load locale"
     _ = lambda x : x
 
 # set global functions
@@ -152,7 +152,6 @@ class MainWindow:
         
         # get scanners in system
         self.sane_devices = sane.get_devices()
-        self.sane_devices_counter = len(self.sane_devices)
         
         # set the scanners combobox
         for device in self.sane_devices:
@@ -205,13 +204,22 @@ class MainWindow:
         
         dialog.destroy()
         
-    def button_preview_clicked_cb(self, obj):
-        "button_preview_clicked_cb activated"
-        
+    def open_scanner(self):
+	if len(self.sane_devices) <= 0:
+          show_error_message(_("No scanners reported by sane"))
+	  raise RuntimeError("No scanners reported by sane\nRecheck your sane configuration")
         # open scanner
         scanner_number = self.config.getint('settings', 'scanner') - 1
+	if scanner_number < 0 or scanner_number >= len(self.sane_devices):
+          show_error_message(_("Bad scanner number %d configured.\nPlease select a valid scanner from the list") % scanner_number)
+	  raise RuntimeError("Invalid scanner %d" % scanner_number)
         scanner = sane.open(self.sane_devices[scanner_number][0])
-        
+	return scanner
+
+    def button_preview_clicked_cb(self, obj):
+        "button_preview_clicked_cb activated"
+        # open scanner
+	scanner = self.open_scanner()
         # options
         options = get_scanner_option (scanner, 'mode')
         if options:
@@ -278,9 +286,7 @@ class MainWindow:
     def button_scan_clicked_cb(self, obj):
         "button_scan_clicked_cb activated"
         # open scanner
-        scanner_number = self.config.getint('settings', 'scanner') - 1
-        scanner = sane.open(self.sane_devices[scanner_number][0])
-        
+	scanner = self.open_scanner()
         # options
         options = get_scanner_option (scanner, 'mode')
         if options:
@@ -529,7 +535,7 @@ class MainWindow:
         # reset settings options
         if scanner_number < len(self.sane_devices):
             try:
-                scanner = sane.open(self.sane_devices[scanner_number][0])
+	        scanner = self.open_scanner()
                 
                 # if scanner exist fill in all the settings