Please try the following:

  1. Open the file \data\avast4.ini, and add the following line to the [WebScanner] section:
    ModifyVistaSocketAutoTuning=0

  2. Save the changes, restart the computer and see if it makes any difference.

If that does not help, try:

  1. Run CMD prompt (as an administrator).

  2. Type:
    netsh interface tcp set global autotunninglevel=disabled

  3. Terminate and restart WebShield. Do you see any difference?