Magento – Trying to get Category URL in Home

I'm trying to get the Category URL in my Home page, I'm working in the file app/design/fronted/[package]/[theme]/template/catalog/product/widget/new/content/new_grid.phtml

I've got this code above the product title

<?php
/**
 * get categories from a product
 */
$categoryIds = $this->helper('catalog/output')->productAttribute($_product, $_product->getCategoryIds());
/**
 * looping through the array of category ids
 */
foreach($categoryIds as $categoryId) {
    $category = Mage::getModel('catalog/category')->load($categoryId);
    if($category->parent_id == 4):
?>
    <h6 class="author"><a href="<?php echo $category->getUrlKey() ?>">De <?php echo $category->getName() ?></a></h6>
<?php
    endif;
}
?>

Some times I use "getUrl" instead of "getUrlKey", and both give me a "404" page.
I believe the error is in some Magento configuration, not in the code.

Some one have an answer to any approach?

Thanks in advence!