New Dev launcher doesn't allow me to play the snapshot, let alone log in...

Bootstrap started
Looking for update
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma
Got reply in: 1592ms
No update found.
Reversing LZMA on C:\Users__\AppData\Roaming\.minecraft\launcher.pack.lzma to C:\Users_\AppData\Roaming\.minecraft\launcher.pack
Unpacking C:\Users__\AppData\Roaming\.minecraft\launcher.pack to C:\Users__\AppData\Roaming\.minecraft\launcher.jar
Cleaning up C:\Users___\AppData\Roaming\.minecraft\launcher.pack
Starting launcher.