fatal errors

I'm new to Drupal and to Openpublish. I'm actually learning the system for my senior project in University. Sadly I am stuck. I've installed Openpublish and have been using their themes and the drupal that comes w/ the module. I fixed the memory errors but now I've gotten several new ones. I can no longer even login into the site to do any sort of fixes. If I try to log in I get this:

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Fatal error: Call to undefined function openpublish_addthis_widget() in /home/koopmand/public_html/drupal3/sites/all/themes/openpublish_theme/page/page.tpl.php on line 96