Chapter 15 Unified Threat Management for FortiOS 5.0 : Web filter : Advanced web filter configurations
  
Advanced web filter configurations
Allow websites when a rating error occurs
Enable to allow access to web pages that return a rating error from the FortiGuard Web Filter service.
If your FortiGate unit cannot contact the FortiGuard service temporarily, this setting determines what access the FortiGate unit allows until contact is re-established. If enabled, users will have full unfiltered access to all web sites. If disabled, users will not be allowed access to any web sites.