Hello
on our old site with Joomla 1.5.26 and K2 2.6.1 we get this warning in category view:

Warning: mysql_num_rows(): 151 is not a valid MySQL result resource in /web/htdocs/www.linkyouth.org/home/libraries/joomla/database/database/mysql.php on line 344

This is an example:
www.linkyouth.org/it/in.html

Can you help us to fix it?

Nothing changed after upgrade to k2 2.6.8

Hi. Have you modified any of the K2 database tables? As i can see in your page, the error is coming from the breadcrumbs module you use there.

Thanks for reply. No, no db changes and no, the warning is still there if I disable breadcrumb module too.

Check for any plugins of group "k2" in the plugin manager. If you find any try to disable them one by one just in case one of them is causing this.