Actually, I have my copy of 1.9 archived, but it's full of mods, texture packs, old saves, and stats. I want a clean slate.
The first time I used the Minecraft launcher, it didn't have this error. It's only on all subsequent attempts to install the game. What's different? Is there a registry key or file I can delete to stimulate it to create a fresh install of Minecraft on this PC?
This is also affecting a friend's laptop. I installed Minecraft a few months ago, he deleted it, and now he bought it but can't install it. Sure, I could copy my binaries over to his machine, but isn't there any other way? What causes the error?