edit:

to solve your problem with this just create a folder named like the path in your message

"C:\Users\MurOnnar\AppData\Roaming\.minecraft\versions\13w16b\13w16b.json"

13w16b

and it works.. thanks to J (down in the comments)

I'm not able to download the latest snapshot.

just message:

Launcher 0.5 (Dev) (through bootstrap 1) started on windows...
System.getProperty('os.name') == 'Windows 7'
System.getProperty('os.version') == '6.1'
System.getProperty('os.arch') == 'amd64'
System.getProperty('java.version') == '1.7.0_17'
System.getProperty('java.vendor') == 'Oracle Corporation'
Delta time to compare resources: 584 ms
Download job 'Resources' skipped as there are no files to download
Job 'Resources' finished successfully
Trying to log in...
Logged in successfully
Getting syncinfo for selected version
Queueing library & version downloads
Couldn't save version info for PartialVersion

java.io.FileNotFoundException: C:\Users\MurOnnar\AppData\Roaming\.minecraft\versions\13w16b\13w16b.json (Das System kann den angegebenen Pfad nicht finden)

-> translation: system could not find the path

at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.<init>(Unknown Source)
at java.io.FileOutputStream.<init>(Unknown Source)
at java.io.PrintWriter.<init>(Unknown Source)
at net.minecraft.launcher.updater.LocalVersionList.saveVersion(LocalVersionList.java:73)
at net.minecraft.launcher.GameLauncher.playGame(GameLauncher.java:94)
at net.minecraft.launcher.ui.sidebar.LoginForm$1.run(LoginForm.java:122)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

maybe old java?