a FATAL ERROR start up bug.

at com.mojang.util.UUIDTypeAdapter.fromUUID(UUIDTypeAdapter.java:22) ~[launcher_mcpatched.jar:?]
at net.minecraft.launcher.game.MinecraftGameRunner.getMinecraftArguments(MinecraftGameRunner.java:285) ~[launcher_mcpatched.jar:?]
at net.minecraft.launcher.game.MinecraftGameRunner.launchGame(MinecraftGameRunner.java:174) ~[launcher_mcpatched.jar:?]
at com.mojang.launcher.game.runner.AbstractGameRunner.onDownloadJobFinished(AbstractGameRunner.java:177) [launcher_mcpatched.jar:?]
at com.mojang.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:122) [launcher_mcpatched.jar:?]
at com.mojang.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher_mcpatched.jar:?]
at com.mojang.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:86) [launcher_mcpatched.jar:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.7.0_65]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.7.0_65]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.7.0_65]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.7.0_65]
at java.lang.Thread.run(Unknown Source) [?:1.7.0_65]
(was i supposed to put that there?)

What I expected to happen was...:
for it to play.

What actually happened was...:
it said this: [17:50:47 FATAL]: Fatal error launching game.

Steps to Reproduce:
1. pressing play
2. going into Development Console
3. then it won't play it says ERROR FATAL