Since there are several of you with the same problem:

  1. Are you all using Avast Internet Security (AIS), and if so what version are you trying to install or use?

  2. Do you have a 3rd party firewall (FW) installed on the machine? If so, you need to uninstall it per the vendor’s instructions prior to installing AIS.

  3. Here is the download file for installing the current version for AIS: http://www.avast.com/en-us/download-software - click on the bottom, 3rd down is AIS

  4. Here is the Avast Uninstaller Tool: http://www.avast.com/uninstall-utility