system
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Windows firewall is disabled.
There’s some good news today, the trying of installing XP and avast 9 one after another succeeded. It is the last combination I made yesterday, I logged in and tried manual update, progress bar still stuck (for program update) or told me on running / up to date (for vps update), and two instup.exe could be seen running. Let it be for tens of minutes, popup balloon message said vps update completed. Check the update tab in UI, version info had been renewed. Clicking the update button then, no more sticking.
It seems that manual update is not recommended before avast accomplishing its self-update attempt. And as the XP above is installed with the same disc, the “unprotected” problem I’ve met may result in some system setting / customization issue (I really did some).