When writing processes to automate some of Magento’s normally laborious tasks, perhaps for a product-import script, a mass attribute update script, category import, or inventory adjustment, keep in mind that you may have to refresh some kind of cache — especially when working with attributes. If you are encountering quirks or inconsistencies with your data, try these:

• Rebuild Catalog Index Mage::getSingleton('catalog/index')->rebuild();

• Rebuild Flat Catalog Product Mage::getResourceModel('catalog/product_flat_indexer')->rebuild();

• Inventory Stock Mage::getSingleton('cataloginventory/stock_status')->rebuild()

If you’ve just upgraded your Magento Commerce site to the 1.4.x release from a 1.3.x release or you using old theme on magneto 1.4.x + , and you forgot to change the theme/template to the default one before you performed the upgrade, you’ll probably end up with a blank white screen.

If we look at line 529 of the “Layout.php” file we can see that it’s itterating over several objects ($this->_output) and producing a coalesced output which can then be displayed on the screen.

/**
* Get all blocks marked for output
*
* @return string
*/
public function getOutput()
{
$out = '';
if (!empty($this->_output)) {
foreach ($this->_output as $callback) {
$out .= $this->getBlock($callback[0])->$callback[1]();
}
}

return $out;
}

In 1.4.x Magento overhauled the templates and themes code so your 1.3.x template/theme isn’t going to work in a 1.4.x environment without some re-coding.  To get over this particular problem, find and edit the ‘page.xml’ file in your template/theme directory.  It should be in ./app/design/frontend/default/{your_theme}/layout/page.xml

Change the line
<block type=”core/profiler” output=”toHtml”/>

to
<block type=”core/profiler” output=”toHtml” name=”core_profiler”/>

Clear the cache directory using “rm -rf magento/var/cache/*” or using admin panel configuration > cache management and refresh your page.  All being well your site should spring back in to life.

If this didn’t work for you, or your template/theme directory doesn’t have a local copy of the ‘page.xml’ file, look at the default files and ensure that they were updated when you upgraded Magento.  You’ll find the files in:

./app/design/frontend/default/default/layout/page.xml
./app/design/frontend/default/modern/layout/page.xml
./app/design/frontend/base/default/layout/page.xml

Hope this helps.