I just activated the w3 total cache plugin and this resulted in a white screen and the inability to get into the admin area. I deleted the plugin folder using FTP.
The error message resulting is:
W3 Total Cache Error: some files appear to be missing or out of place. Please re-install plugin or remove /mnt/stor7-wc2-dfw1/538952/569848/www.reallifenyc.com/web/content/wp-content/advanced-cache.php.
I tried finding this file and couldn't, so I reinstalled the plugin from my backup.
Still a white screen. So I deleted it and got the same error message.