Error message

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/howth/d7.devslashdev.com/modules/block/block.module).