Call to a member function extend() on a non-object in ..../Varien/Simplexml/Config
Fatal error: Call to a member function extend() on a non-object in........./html/lib/Varien/Simplexml/Config.php on line 601.
This error troubles me a lot. It keeps coming again and again often in the back end and in front end as well. Doesn't have any clues to clear those. When this error comes the screen goes blank white page.
I have tried to check and set the file permission for all xml files and others. But no result.
I have tried to analyze for any xml corrupted or any other issues. But couldn't spot the exact file causing this issue. Even the system log doesn't point exactly.