This issue has now been fixed.
When browsing websites via the Sophos Web Appliance, the following result appears: "Blocked request: File is not scannable"
First seen in
Sophos Web Appliance on the 16th May 2014
The reason is linked to a scheduled delay in the latest engine release. This is currently being actioned as at 2am GMT time - 16th May 2014, as a release to update the current Sophos Web Appliance 4.97 engine to version 5.0 for Sophos Web Appliance.
What To Do
Work around for now would be to go to
Configuration > Global Policy > Download Options
and enable/tick “Allow unscannable files”.
The situation is currently being monitored, and this article will be further updated if required.
Please contact Sophos Technical Support if this behaviour persists following the upgrade to version 5.0.
Update: The AV engine update to 5.0 was rolled out to all Web Appliances.