File protection shield cannot be activated

Avast Free Antivirus / Premium Security
1

I have installed the latest version of Avast 2015 free on 29-3-2015.

After restarting and activation the shields, I receive the popup message: the file protection shield cannot be activated. Even after startup for the second time this message appears.

How to solve?

Thanks!

2

What OS/SP ?
What exact version of avast ?
Any other security (related) software installed ? (or did you have it)
Was this a update or a clean installation of avast ?