Manual update doesn't work either (same symptoms). Can't uninstall (nothing happens when I click uninstall/repair from the uninstall control panel). The firewall settings don't contain anything related to Avast setup (it's the default XP firewall). I tried adding Avast to the list of exceptions but that didn't help.
Here's the end of my setup log:
14:37:32 min/gen Started: 30.05.2006, 14:37:32
14:37:32 min/gen Running setup_av_pro-33b (827)
14:37:32 nrm/sys Operating system: WindowsXP ver 5.1, build 2600, sp 2.0 [Service Pack 2]
14:37:32 vrb/sys Computer WinName: X
14:37:32 min/sys Windows Net User: X\Propriétaire
14:37:32 min/gen Cmdline: /downloadpkgs /noreboot /updatevps /silent /progress
14:37:32 vrb/gen DldSrc set to inet
14:37:32 vrb/gen Operation set to INST_OP_UPDATE_GET_PACKAGES
14:37:32 min/gen Old version: 33b (827)
14:37:32 nrm/gen SGW32P::CheckIfInstalled set m_bAlreadyInstalled to 1
14:37:32 vrb/sys Computer DnsName: x
14:37:32 vrb/sys Computer Ip Addr: 192.168.0.166
14:37:32 nrm/int SYNCER: Type: use IE settings
14:37:32 nrm/int SYNCER: Auth: another authentication, use WinInet
14:37:32 vrb/pkg Part prg_av_pro-33b is installed
14:37:32 vrb/pkg Part vps-62104 is installed
14:37:32 vrb/pkg Part news-4a is installed
14:37:32 vrb/pkg Part setup_av_pro-33b is installed
14:37:32 min/gen Old version: 33b (827)
14:37:32 vrb/fil SetExistingFilesBitmap: 814->138->138
14:37:32 min/gen GUID: 28b3cfc3-99a7-4f5e-8c8f-26fed88efd51
14:37:32 min/gen Server definition file for 'main' (C:\Program Files\Alwil Software\Avast4\Setup\servers.def) is invalid.
14:37:32 nrm/pkg Transferred files: 0
14:37:32 nrm/pkg Transferred bytes: 0
14:37:32 nrm/pkg Transfer time: 0 ms
14:37:32 vrb/fil NeedReboot=false
14:37:32 min/gen Return code: 0x2000000C [Can't select any server for downloading (from 0).]
14:37:32 min/gen Stopped: 30.05.2006, 14:37:32
Thanks for your help. Very much appreciated.