Error message

• Warning: Cannot modify header information - headers already sent by (output started at /home/worldcitl/demoeng/website/includes/common.inc:2561) in drupal_send_headers() (line 1040 of /home/worldcitl/demoeng/website/includes/bootstrap.inc).
• PDOException: SQLSTATE[42000]: Syntax error or access violation: 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 'system WHERE type = 'theme' AND status = 1' at line 1: SELECT name FROM {system} WHERE type = 'theme' AND status = 1; Array ( ) in block_flush_caches() (line 904 of /home/worldcitl/demoeng/website/modules/block/block.module).