Website crash following restore attempt: Notice: Undefined variable: attribution in include()

After upgrading to Drupal 7.12 I began experiencing problems with the Calendars. I decided to perform restore from the backup created prior to the upgrade and now cannot get into the site. I placed the site in maintenance mode prior to the upgrade. The following error messages are displayed when accessing the website:

* Notice: Undefined variable: attribution in include() (line 48 of /home/biomedic/public_html/sites/all/themes/corolla/templates/maintenance-page.tpl.php).

* Warning: require_once(/home/biomedic/public_html/sites/all/modules/calendar/includes/calendar_plugin_row_node.inc) [function.require-once]: failed to open stream: No such file or directory in _registry_check_code() (line 3046 of /home/biomedic/public_html/includes/bootstrap.inc).

I recently inherited webmaster responsibilities for the school club and do not have a clue what I'm doing. Any help would be greatly appreciated.