What are you trying to start as avast should run on boot ?
If it is the Simple User Interface for an on-demand scan then I haven’t seen this error for some time and is associated with an old version of avast.
Try a repair of avast. Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button and scroll down to Repair, click next and follow. You need to be on-line to do this.
Check about avast, what is your exact version, the latest is 4.7.986 ?