Magento – Cron not running because of simplexml_load_string error

Try clearing cache, and check file permissions are correctly set,

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Else another alternative is Reinstall Magento and do following steps:

It may solve the issue, but suggested to have round of research before doing and surely back up database:

Before to import database : - Add query

1) SET SQL_MODE=”NO_AUTO_VALUE_ON_ZERO”; 

OR

at beginning of sql import script

After import / installation : - Execute following query

2) SET FOREIGN_KEY_CHECKS = 0;
   UPDATE `core_store` SET `store_id` = 0 WHERE `code` like 'admin';
   UPDATE `core_website` SET `website_id` = 0 WHERE `code` like 'admin';
   UPDATE `customer_group` SET `customer_group_id` = 0 WHERE `customer_group_code` like 'NOT LOGGED IN';
   SET FOREIGN_KEY_CHECKS = 1;

Firstly I had config looking for entity_setup when my folder structure was resource_setup.

The next error came because I had to create an instance of Mage_Eav_Model_Entity_Setup this was done using:

$installer = new Mage_Eav_Model_Entity_Setup('core_setup');