Thank you Geek9. It's not just KB977165, I've manually installed 73 updates after a squeaky-clean install of Win XP Pro SP.3 and some of the logfiles contain similar errors. There is no infection, the pc was offline at all times and no other programs had been installed.
Logfiles of 4 out of 5 updates installed after enabling Automatic Updates also contain error notifications.
The Scan for Latest Updates on the MS Update site shows that all updates are installed.