[tc4me]

Hmm, looks like there's a bug in the actual plugin itself. The developer probably made this plugin for an older PHP version that was less picky about errors and warnings. Newer PHP versions throw warnings for things that older versions ignored, sometimes causing messages like these.

Do you know what PHP version you're using?

I'll take a look and fix it up later today.

Thank you Darth 

I got a tip from doylecc an admin from mybb.de and it works

I looked at the file first.
Just add under line 585:
PHP code:
$ avatars = @opendir (MYBB_ROOT. "/". $ mybb-> settings ['avatardir']. "/". $ directory);

the following one:
PHP code:
$ avatar = array ();