I thought the crash had deleted my backup files, but I was looking at the wrong
drive. I started a new project without incident on a different drive.

Came back to it today and realised I had started the new project on a
different drive and returned to backing up the original set of files. Shortly
after resuming, it crashed again. 

Any ideas? Crash Report:

HTTrack 3.49.2 closed at '.\htscache.c', line 401
Reason: zip_zipCloseFileInZip_failed

Stack trace:
unknown [WinHTTrack]
unknown [WinHTTrack]
coucal_dec [libhttrack]
coucal_dec [libhttrack]
coucal_dec [libhttrack]
coucal_dec [libhttrack]
hts_is_available [libhttrack]
hts_is_available [libhttrack]
copy_htsopt [libhttrack]
copy_htsopt [libhttrack]
hts_main2 [libhttrack]
unknown [WinHTTrack]
htsthread_init [libhttrack]
endthreadex [MSVCR90]
endthreadex [MSVCR90]
BaseThreadInitThunk [KERNEL32]