Check the line 79 in your plugins and themes and find the specific line with the foreach loop.
Then try to find out what the culprit could be.
For example, I got the same error with:
PHP Warning: Invalid argument supplied for foreach() in qa-base.php(595) : eval()'d code on line 161
I found a foreach loop in one of my own plugins on line 161:
foreach($userdata as $metaItem) {
A possible fix is:
if (is_array($userdata)) {
foreach($userdata as $metaItem) {
Hope that helps.