It seems that "Continue interruptted download" not working 
for me...did I not set Httrack correctly?
This time, I first pause the transfer and then selected the 
cancel button in the transfer window (I didnot save 
anything though).  Next time, when I restarted Httrack and 
selected "Continue interruptted downlaod", Httrack rescans 
files, I noticed that it tries to receive every file in the 
link in the transfer window with following syntax:

ftp: receiving /..../../filename

this includes files already downloaded last time and files 
that had problem downloading last time.  However, when I 
open the "File downlaod information" window on the 
receiving file, looks like Httrack receiving every byte of 
the file, however, somehow some parameters looks fishy:

ChunkMode: no
TestMode: no
HeadRequest: no
NotModified: no
WriteToDisk: no
LocalFile: no

It is suspicious for parameters WriteDisk and LocalFile, 
the file actually exists in local hard disk but why Httrack 
still needs to run through every byte of the file.  For the 
file that had problem last time, why doesn't it write to 
hard disk?
I found another issue may be a bug.  Seems that Ctrl+C and 
Ctrl+V, or the correspond copy and paste command do not 
work for Httrack.

Thanks for help.