I may have fixed it... I'm not sure, but HTTrack is downloading what looks like
more content. When it finishes I'll know for sure, but two things I changed
are

1) in my web browser when logging in, I clicked a radio button that said
'remember me'. I think this sent a cookie that kept HTTrack logged in after it
left the welcome-login page. 

2) the other thing I did was remove the filter
-*
so now my only filters are to remove the logout page, and to download the
forum.