Index: app/controllers/my_controller.rb
===================================================================
--- app/controllers/my_controller.rb	(revision 2589)
+++ app/controllers/my_controller.rb	(working copy)
@@ -139,8 +139,8 @@
   # params[:list-(top|left|right)] : array of block ids of the group
   def order_blocks
     group = params[:group]
-    if group.is_a?(Array)
-      group_items = params["list-#{group}"].collect(&:underscore)
+    if group.is_a?(String)
+      group_items = (params["list-#{group}"] || []).collect(&:underscore)
       if group_items and group_items.is_a? Array
         # remove group blocks if they are presents in other groups
         %w(top left right).each {|f|