Windows file system error 00000005 (5) = Access is denied.
This may be because avast's files and registry entries etc are protected by the self-defence module, but I'm not sure that would be the case considering you have done this before. Try again having first disabled the self-defence module.
It could also be permissions based (UAC depending on your OS), so what is your OS ?
Is the account you are running the manual update from one with administrator privileges ?