I had issues too. First off, I run 2 SD cards (I don't trust the update software). I ALWAYS turnoff my anti-virus, that kills it every time.This time it just hung in a loop with 4.5 install. The only thing that fixed it was a format of the SD card and a complete reinstall. Not hard, but a pain. I would suggest everyone keep 2 SD cards, 1 as a backup. I also keep the files on my harddrive.
Hop this helps.
AK