I've run into this myself, and looking across years of forum posts, I've seen
it posted several times with no response from the developer other than
"Antivirus?  Rebooted?"

This error has been reported by multiple macOS users, as well as Linux users -
it's a problem with the program itself.  It'd be nice to see it fixed, but my
guess is if it hasn't happened in the past seven-plus years, don't hold your
breath.

Here's the crux of the problem - httrack doesn't handle IPv6 addresses.  When
it goes to create the local proxy for the CatchURL functionality, it tries to
do those with an IPv6 address but fails since it doesn't understand those
(that's the basic summary of the issue).

You can work around this by disabling IPv6 on your machine and then running
httrack with the --catchurl param and it should work.  Here's how:

<http://help.unc.edu/help/how-do-i-disable-ipv6-on-mac-os-x/>