Very often it may be blocking you from running a program or accessing web page, which you know is totally safe. Some time passes and everything seems be OK. However, in a while the issue can persist again.
Please use every other antivirus software (for example like free Panda Antivirus, A.V.G. or Avira - all of them have free-2- use applications, or any other antivirus software like Eset Smart Security, etc.).
Please notice that we can't asset a new trouble ticket about any network issues if there's Avast still installed on your PC.