I am having the same issue. I checked the about discussed items and I am in
compliance.
Anon FTP is allowed, so I tried via ftp:// etc with the following results:
With HTTrack: same setting above + to protect server load I have limited my
scan to 2 connects at a time, and it still errors out. 
Manually: I can do it with 3 connections at a time, with no problem. Just
significantly more time consuming.
There must be a setting I am missing, any help would be nice.