I attempted an upgrade of my site to 5.6.0.2 but I get the following error after hitting the Upgrade button:

Warning: dom_import_simplexml(): Invalid Nodetype to import in /usr/local/www/concrete5/updates/concrete5.6.0.2/concrete/core/controllers/single_pages/upgrade.php on line 200

Warning: dom_import_simplexml(): Invalid Nodetype to import in /usr/local/www/concrete5/updates/concrete5.6.0.2/concrete/core/controllers/single_pages/upgrade.php on line 201

Fatal error: Call to a member function appendChild() on a non-object in /usr/local/www/concrete5/updates/concrete5.6.0.2/concrete/core/controllers/single_pages/upgrade.php on line 202

I do have the XML extension installed in PHP but haven't been able to figure out why the error message is coming up.