Anybody know a fix for that error? Never saw this one!
Fatal error: Call to a member function extend() on a non-object in /var/www/..../..../lib/Varien/Simplexml/Config.php on line 600
Try clearing cache, and check file permissions are correctly set,
Directories : 755
Files : 644
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;
This page still comes up among the first Google results for the error message reported by the OP. I think it can be useful for others to add my solution, which is different from the accepted one.
The error mentioned in the question can also mean an error in local.xml. So, check /app/etc/local.xml for typos or malformed code.
In my case, while editing this file I left instructions outside the </config>
tag. Moving them before the closing tag solved the issue.