Not sure why the author wont support this feature.  In cases when a server only
supports a limited number of queries per 24 hour period (such as the Google
App engine), it becomes impossible to download the full site, because every
night when the quota is reset, HTTrack tries to download the SAME files.

Here's the solution:

1) Go to the hts-cache folder and open new.txt in Notepad++.  Delete all lines
describing errored downloads. 
2) Open new.zip with Windows Explorer (not WinRAR, because the file contains
special characters that can't be handled by WinRAR).  Delete all the errored
out files within the zip.
3) Run HTTrack again but choose "Continue interrupted download" instead of
"Update files"