Thread:Extension talk:DumpHTML/Error: Unable to copy file/reply (3)

Sorry, can't help you here. It works on Linux (see http://misc.j-crew.de/wiki-dump/current/ for a working example). For reference, I use only the -d and the --image-snapshot option. I fear you'll have to debug this yourself (though I should warn that the whole file access code is quite difficult to follow). Patches to fix this (and other) issues greatly appreciated.