Sometimes the ProxyAV is not able to apply successfully downloaded virus definition file.

In this case login to the ProxyAV appliance and go to Utilities and click on the “Refresh Engine and Signatures” button.
 

It will
1. Delete all engine data and pattern files.
2. Reboots the AV.
3. Downloads a full engine update.

If the problem still persist, contact Bluecoat Technical Support for further assistance.