Minecraft Launcher wont start.

The launcher won't start and I get this error:
FATAL ERROR: net.minecraft.bootstrap.FatalBootstrapError: Unable to un-pack200: java.io.FileNotFoundException: C:\Users\Joe\AppData\Roaming\.minecraft\launcher.jar (The process cannot access the file because it is being used by another process)
at net.minecraft.bootstrap.Bootstrap.unpack(Bootstrap.java:159)
at net.minecraft.bootstrap.Bootstrap.execute(Bootstrap.java:123)
at net.minecraft.bootstrap.Bootstrap.main(Bootstrap.java:381)

EDIT:
After submitting this bug report, it worked!