Yea i had the exact same problem and had to roll back from 1511 to then completely remove Avast before applying that update again.
The issue then is that when you do update to 1511 you will most likely run into issues with getting Avast Endpoint back onto that machine, main problem is that the Firewall Service just does not start which is not good.
The problem is that if any Avast product was installed previously i got this issue, only solution i could find was a complete re-install of the OS, get it onto Windows 10 1511 build before installing Avast. Which for me was not a solution and instead i migrated over to the newer Cloud Version of the product.
Cloud Version still has problems but at least with this version there is hope they will get fixed.