> 15:12:38	0/-1	-R-M--	416	error
> ('Requested%20Range%20Not%20Satisfiable')	text/html

This one should be handled by httrack.

> 15:12:40	63/63	-R-M--	412	error
> ('I%20do%20not%20accept%20If-Unmodified-Since')

Humm, it means that the remote server isn't able to handle 
if-unmodified-since, and is not responding correctly to the 
request :(

I'll try to find a workaround, but it's not totally obvious 
to do.