I just found this community while looking for the solution to my problem with HTTRACK, and I've noticed many people before me have had this same problem.
I am trying to download the full contents of a particular site to add to my archives all at once (it would take ages to download all of the individual webpages as PDF files manually) and find it impossible to do it with HTTRACK because it keeps displaying the Mirror Error.
I've tried everything I could already, scoured all the forums and read all of the forum posts on this issue, and nothing that has been suggested has worked so far.
MIRROR ERROR!
HTTrack has detected that the current mirror is empty. If it was an update,
the previous mirror has been restored. Reason: the first page(s) either culd
not be found, or a problem occured.
=> Ensure that the website still existsand/or check your proxy settings! <=
I tried using other tools but haven't had any luck. Cyotek's Webcopy doesn't go deep enough into the site's layers. Or at least I couldn't make it do it.
The solution is here. The site maybe wrongly redirecting httrack because of its default user agent so change httrack's browser id/identity. Did you check the webcopy log for errors, it may be site blocking the app and if that is the case, you will also get the same issue with httrack.