Civicrm fails to launch - Wordpress gives "The plugin does not have a valid header."
As regarrds the error message "You do not have sufficient permissions to access this page", please have a look at the Civicrm wiki page at the following link.  https://wiki.civicrm.org/confluence/display/CRMDOC/Upgrading+CiviCRM+for+Wordpress

If you get this error when trying to run the upgrade script, you most likely deactivated CiviCRM plugin during the upgrade process. You just have to visit /wp-admin/plugins.php and activate the plugin.

I  regret I can't help with the "valid header" problem.

Hope this helps.