So, I don't know why I didn't experience this on my flash drive, but it happened on my external hard drive. Not sure why.
I can't recall, but doesn't the Platform installer force the running Platform closed? It didn't do that and threw itself into a loop. Had to use Task Manager to quit (neither would allow me to).
No big deal, I just downloaded the new Platform installer manually. And, that worked perfectly.
Did you upgrade within the platform itself? How many processes are running on your system? There's a bug in the NSIS processes plugin that causes it to fail if too many are running. I'm gonna patch that at some point.
Sometimes, the impossible can become possible, if you're awesome!