[Plugin: PictureGrid] plugin not working in firefox

I succesfully tested the plugin with IE6, IE7, OPERA and SAFARI.

But in FIREFOX I get an error:

Warning: Invalid argument supplied for foreach() in /home2/../wp-content/plugins/picturegrid/picturegrid.php on line 213

Any clue why this is happening? Any solution?

http://wordpress.org/extend/plugins/picturegrid/