If you are trying an external script in Magento but are unable to complete the task and are getting the above error. Tasks such as deleting a customer will throw this error. The solution is this:
Use the below code after including the file “app/”
Mage::register(‘isSecureArea’, true); /* set secure admin area*/
Mage::getModel(‘review/review’)->load($review)->delete(); /* Your operation */
Mage::unregister(‘isSecureArea’); /* un set secure admin area*/
And that it! you can now run tasks that usually would require admin login, in your script.