Thanks very much Darren Melanson​, I can confirm that it works for me on High Sierra too, which is great! Only one thing -- I noticed that the download for the packager tool linked to from the UK version of the support page (https://helpx.adobe.com/uk/digital-publishing-solution/help/install.html) still points to the old version, so I imagine this means that other localised support pages are also still pointing to the old version too.

Great news, thanks very much!

Hi Darren Melanson​, is there any ETA on a fix for this issue yet? Thanks!

Hi Darren Melanson​, thanks for the quick reply. FWIW, it might just be that the tool needs recompiling against an updated version of Go -- there's a host of similar-sounding issues on the Go GitHub issues tracker: https://github.com/golang/go/search?utf8=%E2%9C%93&q=MSpanList_Insert+macOS&type=Issues Please do keep me posted on progress -- I'm having to rely on a Windows virtual machine to use the packager tool at present.Thanks!