3.9 plugin issues

Did a manual upgrade to v 3.9 because client’s server set up won’t allow one-click upgrade.

Now, I’m having plugin issues. The plugins section won’t load properly and the following is showing:

Warning: Invalid argument supplied for foreach() in /usr/www/users/pl719/MCHA/wp-includes/plugin.php on line 622

It’s displaying on every page of the dashboard at the top and multiplies with every plugin activated (IF I can get them to activate).

Please advise.