/// 

      /// Generic method to load information in a DropDownList control.
      /// 
      /// DropDownList control.
      /// List to get data.
      /// Column to get the text for the elements.
      /// Column to get the value for the elements.
      /// This DropDownList control is necessary for fill the DropDownList.
      /// Column to filter values from the DropDownList that depends on.
      private void LoadDropDownList( DropDownList ddl, SPList list, string titleField, string valueField, 
         DropDownList ddlDependsOn, string filterField )
      {
         if ( ddlDependsOn.SelectedIndex < 1 )
         {
            ddl.Items.Clear();
            ddl.Enabled = false;
         }
         else
         {
            ddl.Enabled = true;
            ArrayList elements = new ArrayList();
            ListItem li = new ListItem();
            li.Text = "No filtrar";
            li.Value = "0";
            ddl.Items.Add( li );
            for( int i = 0; i < list.ItemCount; i++ )
            {
               li = new ListItem();
               try
               {
                  string filter = "";
                  if ( null == list.Items[i].ContentType.Fields.GetField(filterField) )
                     filter = list.Items[i][list.Items[i].Fields[filterField].InternalName].ToString();
                  else
                     filter = list.Items[i][list.Items[i].ContentType.Fields[filterField].InternalName].ToString();
                  if ( filter.Trim().CompareTo( ddlDependsOn.SelectedItem.Text.Trim() ) == 0 )
                  {
                     if ( null == list.Items[i].ContentType.Fields.GetField(titleField) )
                        li.Text = list.Items[i][list.Items[i].Fields[titleField].InternalName].ToString();
                     else
                        li.Text = list.Items[i][list.Items[i].ContentType.Fields[titleField].InternalName].ToString();
                     if ( null != list.Items[i].Fields.GetField( valueField ) )
                        li.Value = list.Items[i][list.Items[i].Fields[valueField].InternalName].ToString();
                     else
                        li.Value = list.Items[i][list.Items[i].ContentType.Fields[valueField].InternalName].ToString();
                     if ( !elements.Contains( li.Text ) )
                     {
                        elements.Add( li.Text );
                        ddl.Items.Add( li );
                     }
                  }
               }
               catch ( Exception )
               {
                  // This exception is for the elements that are in blank or doesn't exists.
               }
            }
         }
      }