After a database was corrupted and reloaded from a backup. Looking at the error log this appears to be where CiviCRM is hanging.
Here is the debug information.
[debug_info] => CREATE TEMPORARY TABLE civicrm_temp_group_contact_cache1632 (SELECT 95 as group_id, contact_a.id as id FROM civicrm_contact contact_a LEFT JOIN civicrm_email ON (contact_a.id = civicrm_email.contact_id AND civicrm_email.is_primary = 1) WHERE ( ( (NULLIF(civicrm_email.email, '') IS NOT NULL) AND contact_a.do_not_email = AND contact_a.is_opt_out = AND contact_a.contact_type = 'Individual' ) ) AND (contact_a.is_deleted = 0) AND contact_a.id NOT IN ( SELECT contact_id FROM civicrm_group_contact WHERE civicrm_group_contact.status = 'Removed' AND civicrm_group_contact.group_id = 95 ) ); [nativecode=1064 ** You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND contact_a.is_opt_out = AND contact_a.contact_type = 'Individual' ) ) AND ' at line 1]
Any advice on how to resolve this is appreciated.