I was trying to apply Windows XP SP3 through windows auto updates.  Auto update repeatedly reported that it couldn’t apply SP3 update. After digging further, I found that update was failing because laptop was not on AC supply.

Two points to note:

1. On laptop, shouldn’t apply windows update while battery powered
2. Interesting to understand that either xp auto update do not have way to report correct problem and instead just say “Could not apply following updates”, or maybe SP3 installer is not rightly coded for auto update.