I want to mirror a website that needs a login via form. I understand I have to
use --catchurl to do that (non-GUI version).

Whenever I try "httrack --catchurl" in Terminal I get the error: 

"Unable to create a temporary proxy (no remaining port)"

(Browser is Safari or Chrome on OSX El Capitain. Using latest httrack on brew.
No antivirus in place. Firewall was off.)

This is a known problem. In the forum there was one answer from 7 years ago:
"To capture, you temporarily point your browser to use httrack as a proxy.
httrack's proxy info will be your machine plus port address since it's
running
on your machine." No idea what that means.

Hope someone can help?