when running this command:
httrack -v <https://www.materialpalette.com/>

i also get this error:

Mirror launched on Sat, 31 Dec 2016 16:33:54 by HTTrack Website Copier/3.48-21
[XR&CO'2014]
mirroring <https://www.materialpalette.com/> with the wizard help..
16:33:54	Warning: 	Cache: damaged cache, trying to repair
16:33:54	Warning: 	Cache: 0 bytes successfully recovered in 0 entries
16:33:54	Warning: 	Cache: error trying to open the cache
16:33:54ps://wwwWarning: paletteRetry after error -5
(error:00000001:lib(0):func(0):reason(1)) at link
<https://www.materialpalette.com/> (from primary/primary)
16:33:54ps://wwwWarning: paletteRetry after error -5
(error:00000001:lib(0):func(0):reason(1)) at link
<https://www.materialpalette.com/> (from primary/primary)
16:33:54ps://wwwError: a"error:00000001:lib(0):func(0):reason(1)" (-5) after 2
retries at link <https://www.materialpalette.com/> (from primary/primary)
16:33:54	Warning: 	No data seems to have been transferred during this session!
: restoring previous one!
Done.
Thanks for using HTTrack!

but this works:

curl
<https://www.materialpalette.com/webpack/application-7e0b08b176e2f6c418e9.css>

curl 7.51.0 (x86_64-apple-darwin16.0) libcurl/7.51.0 SecureTransport
zlib/1.2.8