I think igor wanted to ask you if there is any file with exactly 157,598 bytes into the avast folder (C:\Program files\Alwil …) or its subdirectories. Probably, he’s trying to know what file (if any) is causing the error, i.e., it downloads and ‘freezes’ the update proccess. Maybe he wants to know other thing :
Did you try to ‘repair’ the installation through the Control Panel?
Control Panel > Add/Remove Programs > avast antivirus > Change > Choose Repair function
Hope this help 