> Yesterday, I tested on two different proxies, this 
did 
> not work always with a very long file name.

Still the same strange errors in the logs?
> I do not understand your phrase : 'If this does not 
> work, use the 'URL list' option - argv/argc may have 
> limits'. On 'URL List Option', we cannot change the 
> URL Size. What about argv/argc ?
There is an 'URL list' field in WinHTTrack which allow 
you to download all links from a raw text file, such 
as:
<http://www.foo.com/bar>
<http://www.foo.com/foo>
..

By passing the URLs through a text file, and not using 
the commandline, you can bypass the commandline size 
limit (URLs from the text file are merged directly in 
the engine stack).

Another problem may be due to the proxy: many proxies 
are limiting the URL size - can you try to launch the 
mirror without any proxy?