Phalcon Transaction Manager getting 500 server error when rollback is triggered

Phalcom Transaction Manager getting 500 server error when rollback is triggered

https://drive.google.com/file/d/0B7AtJVATjxPFTDktdFFuRXlFM3c/view?usp=sharing

    $request = new Request();
    $guid = new Guid();
    $transactionManager = new TransactionManager();
    $transaction = $transactionManager->get();

    if($request->isPost()){

        $directoryid    = $guid->GUID();
        $memberid       = $request->getPost('memberid');
        $directorytitle = $request->getPost('directorytitle');
        $path           = $request->getPost('path');

        $findfolder = Membersdirectory::findFirst("directorytitle = '".$directorytitle."' AND path = '". $path ."'");
        if($findfolder){
            $data = array('error' => 'Folder is already exist!', 'statuscode' => 400 );
        }
        else{
            try {
                    $savefolder = new Membersdirectory();
                    $savefolder->setTransaction($transaction);

                    $savefolder->directoryid    = $directoryid;
                    $savefolder->memberid       = $memberid;
                    // $savefolder->directorytitle = $directorytitle;
                    $savefolder->path           = $path;
                    $savefolder->datecreated    = date('Y-m-d H:i:s');

                    if($savefolder->save()){
                        $data = array('success' => 'New folder successfully created!', 'statuscode' => 200 );
                        // $transaction->rollback();
                    }
                    else{
                        $data = array('error' => 'Something went wrong!', 'statuscode' => 400 );
                        $transaction->rollback();
                    }

                     $transaction->commit();

                } 

                catch (Phalcon\Mvc\Model\Transaction\Failed $e) {
                    echo "Failed, reason: ", $e->getMessage();
                }

        }

        echo json_encode($data);

    }