Can not set up SugarCRM on localhost

I am trying to set up SugarCRM 7.9 on local system. But I am getting following error :

Fatal error: Class 'Doctrine\DBAL\TransactionIsolationLevel' not found in C:\xampp\htdocs\pss\vendor\doctrine\dbal\lib\Doctrine\DBAL\DriverManager.php on line 181

Fatal error: Uncaught Error: Cannot declare self-referencing constant 'Doctrine\DBAL\TransactionIsolationLevel::READ_UNCOMMITTED' in C:\xampp\htdocs\pss\vendor\doctrine\dbal\lib\Doctrine\DBAL\DriverManager.php:181 Stack trace: #0 C:\xampp\htdocs\pss\include\database\DBManagerFactory.php(158): Doctrine\DBAL\DriverManager::getConnection(Array) #1 C:\xampp\htdocs\pss\include\database\DBManager.php(459): DBManagerFactory::createConnection(Object(MysqliManager)) #2 C:\xampp\htdocs\pss\include\database\MysqlManager.php(304): DBManager->getConnection() #3 C:\xampp\htdocs\pss\modules\DynamicFields\DynamicField.php(109): MysqlManager->tableExists('fields_meta_dat...') #4 C:\xampp\htdocs\pss\include\SugarObjects\VardefManager.php(728): DynamicField->buildCache('Administration', false) #5 C:\xampp\htdocs\pss\include\SugarObjects\VardefManager.php(1074): VardefManager::refreshVardefs('Administration', 'Administration', NULL, true, Array) #6 C:\xampp\htdocs\pss\data\SugarBean.php(527): VardefManager::loadVardef('Administration', 'Admi in C:\xampp\htdocs\pss\vendor\doctrine\dbal\lib\Doctrine\DBAL\DriverManager.php on line 181

I am not getting what is wrong? Please help.

Thanks,

Shantanu