I tried to enable both the fixed amount coupon module and the percentage module at the same time. I got this error. After I tried to enable them separately it worked fine.

Uncaught exception thrown in session handler.

PDOException: SQLSTATE[HY000]: General error: 2014 Cannot execute queries while other unbuffered queries are active. Consider using PDOStatement::fetchAll(). Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute.: SELECT 1 AS expression FROM {sessions} sessions WHERE ( (sid = :db_condition_placeholder_0) AND (ssid = :db_condition_placeholder_1) ) FOR UPDATE; Array ( [:db_condition_placeholder_0] => ekG50y_pINnNgP2UOHGlGyezB8D-kVMZ4AJPbHTtFXY [:db_condition_placeholder_1] => ) in _drupal_session_write() (line 209 of /var/www/slow/wholebox.org/www/includes/session.inc).

Uncaught exception thrown in shutdown function.

PDOException: SQLSTATE[HY000]: General error: 2014 Cannot execute queries while other unbuffered queries are active. Consider using PDOStatement::fetchAll(). Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute.: DELETE FROM {semaphore} WHERE (value = :db_condition_placeholder_0) ; Array ( [:db_condition_placeholder_0] => 185734530450e9516556de32.73923255 ) in lock_release_all() (line 269 of /var/www/slow/wholebox.org/www/includes/lock.inc).