Error in manage category Magento CE 1.8

Question

I installed a fresh copy of magento CE1.8 on my system. I was able to add a few categories and products. But, all of a sudden the manage category page started showing an error

Fatal error: Class 'Mage_Adminhtml_Block_Catalog_Category_Tree' not found in C:\wamp\www\magento\app\code\core\Mage\Core\Model\Layout.php on line 491

I have not modified any code at all. Cant understand why this stopped working.

Answer 1

Try to run compilation process

compilation process copies all of the class definitions and code found under app/code into a singe directory: includes/src/ to increase magento performance. The performance increase is between 25%-50% on page loads.