I get an error when I am trying to show a category, everything works but the error is visible in the bottom on the page.

Warning: mysqli_close() [function.mysqli-close]: Couldn't fetch mysqli in /var/www/training/libraries/joomla/database/database/mysqli.php on line 148

On row 148 in mysqli.php it sais:
mysqli_close($this->connection);

Can somebody help me with this?

I have the same issue.

I had the same issue and i figure it out why it was showing a warning. What i did to resolve this issue was following. Check under K2 -> users and if u have users there that don't belong to any K2 user groups if so try creating a group and assign user to that group and the warning should go away.

Note that there are 2 columns "Joomla! Group" and "Group" u should look at the second one and if it's empty do the thing i mentioned and u should get rid of the warning.

Hope this helps.

Thanks Alen,

I made sure all of my users belonged to a K2 category and then cleared the Joomla cache and they were gone. I don't know if this will help anyone else but I had transfered alot of those users with SP Upgrade from a Joomla 1.5 site so I just opened then and saved them again and that seem to do the trick.

Cheers