Comment 15 for bug 834619

I had to patch Magento 1.6.1 to be able to export product (which include getting the list of product_links).

In app/code/core/Mage/Catalog/Helper/Product.php :

public function getProduct($productId, $store, $identifierType = null) {
        $loadByIdOnFalse = false;
        if ($identifierType == null) {
            // Magento 1.6.1 : if (is_string($productId) && !preg_match("/^[+-]?[1-9][0-9]*$|^0$/", $productId)) {
            if (is_string($productId)) {
                $identifierType = 'sku';
                $loadByIdOnFalse = true;
            } else {
                $identifierType = 'id';
            }
        }