> Two problems detected:
> - the site does not properly handle keep-alive
> - httrack does not properly handle broken keep-alive, and 
> will not issue any retry
> 
> I will fix this problem (fixed in the current beta-7 for 
> Unix/Linux) soon, among with other details

And I forgot to mention:
As a temporary fix, disable the keep-alive feature in 
httrack (see options) ; this should do the trick