Fatal error - call to a member function failed

On node/add page, page breaks and following error shows for non-admin users only.

Fatal error: Call to a member function uses_row_plugin() on a non-object in /home/xxx/public_html/sites/all/modules/advanced_forum/advanced_forum.module on line 526

When I comment lines between 523 to 594 in advanced_forum.module file, the error goes away but it is not a permanent solution.