Definitely shows up as fully downloaded. I have deleted and re-downloaded several different Platform Packs with exactly the same outcome. I get the same pop up screen as tbjorn81 posted above. Also as mentioned, I made sure my language and location settings were English/US and had my antivirus completely disabled. (at one time, I actually removed my antivirus, restarted and tried again with the same result)
Any other ideas I can try??