DB Error: Commands out of sync; you can't run this command now

Stack Trace:

File: C:\xampp\htdocs\vhost\journal\ojs\classes\session\SessionDAO.inc.php line 30
Function: DAO->retrieve("SELECT * FROM sessions WHERE session_id = ?", "b91nmq681kmqenilg2i2093n21")

File: C:\xampp\htdocs\vhost\journal\ojs\classes\session\SessionManager.inc.php line 144
Function: SessionDAO->getSession("b91nmq681kmqenilg2i2093n21")

File: (unknown) line (unknown)
Function: SessionManager->read("b91nmq681kmqenilg2i2093n21")

File: C:\xampp\htdocs\vhost\journal\ojs\classes\session\SessionManager.inc.php line 57
Function: session_start()

File: C:\xampp\htdocs\vhost\journal\ojs\classes\session\SessionManager.inc.php line 106
Function: SessionManager->SessionManager(Object(SessionDAO))

File: C:\xampp\htdocs\vhost\journal\ojs\classes\security\Validation.inc.php line 283
Function: SessionManager::getManager()

File: C:\xampp\htdocs\vhost\journal\ojs\classes\core\Request.inc.php line 707
Function: Validation::isLoggedIn()

File: C:\xampp\htdocs\vhost\journal\ojs\includes\driver.inc.php line 98
Function: Request::isCacheable()

File: C:\xampp\htdocs\vhost\journal\ojs\index.php line 97
Function: require("C:\xampp\htdocs\vhost\journal\ojs\includes\driver.inc.php")