I have a store that uses file based sessions. All seems to be working for a while then suddenly When I add to cart I am redirect to a 404 page with the follow error in the url :
Fatal error: Class ‘Mage’ not found in /var/www/app/code/core/Mage/Core/functions.php on line 0
At this point the backend admin no longer works and reports the same error.
the only way I can clear this is to remove all of the sessions files from ./var/session directory.
Having tested the site seems stable when using a databased based session.
Has anyone else come across this? I would be interested in anyones thoughts as to what might be going on here and any potential solutions that I could test.