         for (i = 0; i < n; i++)
         {
             // skip any columns that are visible
-            if (skipVisible && j < visibleColumns.length && visibleColumns[j].colNum == columns[i].colNum)
+            if (skipVisible && j < visibleColumns.length && visibleColumns[j].colNum == _columns[i].colNum)
             {
                 j++;
                 continue;
             }
-            c = columns[i];
+            c = _columns[i];
 
             if (!c.visible)
                 continue;

            }

            var newAbsoluteColumnIndex:int = displayToAbsoluteColumnIndex(newDisplayColumnIndex);
            if (newAbsoluteColumnIndex < 0 || newAbsoluteColumnIndex > columns.length-1)
                return -1;

            if (scroll)

                    var lockedWidth:Number = 0;
                    if(lockedColumnCount > 0)
                    {
                        var lastLockedInfo:AdvancedDataGridHeaderInfo = getHeaderInfo(_columns[lockedColumnCount-1]);
                        lockedWidth = lastLockedInfo.headerItem.x + _columns[lockedColumnCount - 1].width;
                    }
                    else
                        lockedWidth = 0;
