128
Maybe try sql debug, see if there are any queries in red, which are queries that failed to execute.
If you need the sql query to change the debug setting, and assuming you are using XOOPS 2.0.x :
UPDATE xoops_config SET conf_value=2 WHERE conf_name = 'debug_mode'
Change "xoops" to your prefix if it's different, of course.
If you are using 2.2.x I can't help you, haven't looked at the config settings there.