Error in mysql.php on line 344

If I understand you correctly, you're asking me to limit the amount of items showed when the directory link is clicked. I did this (set it to 25) and I still receive the same error:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in .../libraries/joomla/database/database/mysql.php on line 344

try to 10 for testing

Nope, I still get the same error, even at set at 10.

do you have some plugin in your content ?