I downloaded the latest VPS update "Update 4.x VPS (released: 7.11.2008, version: 081107-0) "
and an error occured :
Error message:
can’t install vps update please report following errorcodes.
ver:4.8.1229
SI:0x00000005
ST:0x00000000
LE:0x00000000
thanks in advance
sarper
Welcome to the forum 
Error 5 is access denied.
What is your OS? (WinXP, Vista?)
Are you logged in as an administrator or a common user on your computer?
Please, post the last 300-350 lines of avast log: C:\Program Files\Alwil Software\Avast4\DATA\log\Setup.log
Try out solution from this post.