Well Lukor's instructions aren't complex but I shall expand them.
1) turn the proxy off
double click the avast icon, in the on-access scanners list, select the Web Shield provider and click Terminate. You will be asked if you want to persist the changes, answer No.
2) edit avast4.ini, in the section [WebScanner] add OptinProcess=admunch.exe
The file is in this location "C:\Program Files\Alwil Software\Avast4\DATA\avast4.ini", first copy the file and save it in another folder so if you mess up (unlikely) you have a copy.
Open the avast4.ini file using a text editor like notepad.
Find the section starting with [WebScanner] and add this line "OptinProcess=admunch.exe" (without the quotes) and save the file and exit.
3) restart webshield
double click the avast icon, in the on-access scanners list, select the Web Shield provider and click Start. You will be asked if you want to persist the changes, answer Yes.