Hi Efjee,
I have a same problem after upgrade my MaxOS to new version 10.9.3, after that my installed avast can’t connected to my account and the shields was disable. So i remove the installed avast and then re-installed again, and recently my avast is working properly.
You may try following my experience, it maybe can help you to solve the problem. As for your additional information i am using avast 8.0 (40795) version.