You must have to put your images in media folder and est full path. Please check the below code i changed.
<?php
require_once 'app/Mage.php';
Mage::app();
Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
$importDir = Mage::getBaseDir('media') . DS . 'bulkimages/101/';
$productsData = array('Purple-Crown-Ring-MFAS.jpg','Purple-Crown-Ring-MFC.jpg','Purple-Crown-Ring-MSAS.jpg','Purple-Crown-Ring-MSF.jpg');
$productSKU = '111';
$ourProduct = Mage::getModel('catalog/product')->loadByAttribute('sku',$productSKU);
foreach($productsData as $fileName){
$filePath = $importDir.$fileName;
if (file_exists($filePath)) {
$ourProduct->addImageToMediaGallery($filePath, array('image', 'small_image', 'thumbnail'), false, false);
$ourProduct->save();
echo "done ";
} else {
echo $productSKU . " not done";
echo "<br>";
}
}
?>