Seeing you’re using Internet security my bet is on the Firewall. See my thread about the issue.

A few things you can try:

  • Turn off windows firewall if it’s somehow still active and conflicting with Avast’s firewall
  • Repair the Avast installation (via (un-)installer) or remove → clean → re-install
  • Last resort: Remove the Avast IS firewall and use the Windows firewall (see instructions in the linked thread)