I got X3 via DVDs hoping to avoid such difficulties. No way! Having spent about an hour in a recursive programme loop of frustration and despair I unfortunately had to apply a zero-level interrupt to my brain and force a hard reset - beer works best for me, I find! (Feeling much better now, thanks)
For the record, the XLN Installer responds with: "ERROR File download failed! Please check your internet connection and try temporaily disabling firewall or anti-virus apps...Cotton XLN Online Installer/1001/InstallData_app_ad/FactoryPresets/AD/PopRock/MediumSmack n Pop.ADPreset". Obviously this message would be unintelligible to the layman, but luckily I have worked with IT professionals over many years, so I can interpret. Translated, it means: "Go away, you are an idiot and we don't want your business. We have expensive toys to play with, leave us alone". No problem. XLN won't be getting any more business of mine!