Error while calling MysqlHelper.ExecuteNonQuery on a store procedure with a OUT parameter. (no replies)

Error when using MysqlHelper.ExecuteNonquery on a stored procedure with OUT parameter
----------
string string procSaveNotificationClickTime = "call test.save_user_alert_last_read_time(@p_user_id,@p_last_read_time,@r_return)";
string connectionString = ConfigurationManager.ConnectionStrings["testdb"].ConnectionString;
MySqlParameter[] parameters = new MySqlParameter[3];
parameters[0] = new MySqlParameter("@p_user_id", al.uid);
parameters[1] = new MySqlParameter("@p_last_read_time", lastReadTime);
parameters[2] = new MySqlParameter("@r_return", MySqlDbType.Int32);
parameters[2].Direction = ParameterDirection.Output;

retCode = MySqlHelper.ExecuteNonQuery(connectionString, procSaveNotificationClickTime, parameters);

----------

Get following error:"OUT or INOUT argument 3 for routine test.save_user_alert_last_read_time is not a variable or NEW pseudo-variable in BEFORE trigger"