Hello,
we are currently having a problem with installation - unfortunately we had a bug in our release process of scanning engine which caused an incomplete engine to be deployed for download. The client detect this and ignores it, however this causes install to fail. We are working on fixing this, hopefully it should be fixed soon. Please try to install Avast a bit later (NOTE: you may need to delete avast directory via command
rm -rf "/Library/Application Support/Avast"
before trying that to get rid of the "avast already installed" error and to progress further through the installation).
The issue discussed in this thread originally is not relevant to this issue.
We appologize for the inconvenience.
Kind regards,
Ondrej Kolacek