Drupal 7 errors after upgrading from 7.12 to 7.14
I ran into the same issue and found the solution here: http://drupal.org/node/1427430

Do you happen to also have the opengraph_meta module installed?
If so just edit this file: 

sites/[your-site]/modules/opengraph_meta/opengraph_meta.module


search for this line:

'#attributes' =&gt; array('class' =&gt; 'opengraph-thumbs-wrapper clearfix'),


and change it to look like this one:

'#attributes' =&gt; array('class' =&gt; array('opengraph-thumbs-wrapper','clearfix')),