Can not update Avast! Please!!!

[Garfild]

 I have searched previous similar posts and tried the advice but it didn't fixed the problem!PLEASE FOR HELP!
When attempting to update Avast it shows: "Unable to update. Last encountered error:The parameter is incorrect."
I tried what was proposed in a previous post - reinstalled it, with downloading it again, but the problem stayed! It's same for the program update and virus database update. My current virus database is 081204-0. 12/04; Windows XP, 4.0 Home edition, Windows firewall's on, Spybot Search and Destroy installed(but it malfunctions too).
It keeps showing red notification that I'm using old virus database and that my anti virus may be out-of-date.
PLEASE FOR HELP!!!
Thanks!

[Lisandro]

Please, post the last 300-350 lines of avast log: C:\Program Files\Alwil Software\Avast4\DATA\log\Setup.log
Also, which is your firewall? Did you have any other antivirus before avast? Which one? How did you uninstall it?