Hi reboot did not have any effect. The version I have is 17.9.2322 build 17.9.37610 released on the 21/12/2017 Avast Premium. The previous release worked fine.
This is the same problem reported by kathandaland but the restart did not correct the problem. The problem was solved using the solution suggested by Asyn
Repair Avast:
1. Control Panel -> Add/Remove programs -> Avast
2. Click on 'Repair'.
3. Follow instructions.
4. Reboot.