SHOUTING (all caps) isn't required.
This is enabled by default, so unless you have been tweaking the avast5,ini as suggested in this topic it should be there.
Your image shows a pretty sparse set of extensions, do you actively try to keep them to a minimum ?
If so that could be the cause and an area to look at.
If not:
- Try a repair of avast:
XP - Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and select Repair, click next and follow.
Vista, win7 - Control Panel, Programs & Features, uninstall a program, select 'avast! Anti-Virus,' click the Change/Remove button and select Repair, click next and follow.
You may need to reboot after the repair.