Problème de launcher

Bonjour à tous.

Je vous écris car je suis nouveau sur minecraft.
Au passage merci pour les topics et les tutos qui m'ont bien aidés.

Je peine depuis un petit moment pour installer des mods.
Par exemple je me suis pris le mods MutantCreatures-1.7.10-1.4.8.
J'ai bien la bon version de forge, java est a jour, j'ai même essayé avec legacyjavafixer-1.0.

Mais mon launcher ne veux rien savoir il s'arrète en me faisant :

[10:47:34] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[10:47:34] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[10:47:34] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
[10:47:34] [main/INFO] [FML]: Forge Mod Loader version 7.10.85.1277 for Minecraft 1.7.10 loading
[10:47:34] [main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_25, running on Windows 8.1:amd64:6.3, installed at C:\Program Files (x86)\Minecraft\runtime\jre-x64\1.8.0_25
[10:47:34] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[10:47:34] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker
[10:47:34] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[10:47:34] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[10:47:34] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.relauncher.CoreModManager$FMLPluginWrapper
[10:47:35] [main/INFO] [FML]: Found valid fingerprint for Minecraft Forge. Certificate fingerprint e3c3d50c7c986df74c645c0ac54639741c90a557
[10:47:35] [main/ERROR] [FML]: The minecraft jar file:/C:/Users/Romain/AppData/Roaming/.minecraft/versions/1.7.10-Forge10.13.2.1277/1.7.10-Forge10.13.2.1277.jar!/net/minecraft/client/ClientBrandRetriever.class appears to be corrupt! There has been CRITICAL TAMPERING WITH MINECRAFT, it is highly unlikely minecraft will work! STOP NOW, get a clean copy and try again!
[10:47:35] [main/ERROR] [FML]: For your safety, FML will not launch minecraft. You will need to fetch a clean version of the minecraft jar file
[10:47:35] [main/ERROR] [FML]: Technical information: The class net.minecraft.client.ClientBrandRetriever should have been associated with the minecraft jar file, and should have returned us a valid, intact minecraft jar location. This did not work. Either you have modified the minecraft jar file (if so run the forge installer again), or you are using a base editing jar that is changing this class (and likely others too). If you REALLY want to run minecraft in this configuration, add the flag -Dfml.ignoreInvalidMinecraftCertificates=true to the 'JVM settings' in your launcher profile.
Exception in thread "main" [10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: java.lang.ExceptionInInitializerError
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.common.asm.FMLSanityChecker.call(FMLSanityChecker.java:159)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.common.asm.FMLSanityChecker.call(FMLSanityChecker.java:39)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.relauncher.CoreModManager$FMLPluginWrapper.injectIntoClassLoader(CoreModManager.java:126)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at net.minecraft.launchwrapper.Launch.launch(Launch.java:115)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: Caused by: java.lang.NullPointerException
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.common.Loader.<init>(Loader.java:182)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.common.Loader.instance(Loader.java:160)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.common.FMLCommonHandler.<init>(FMLCommonHandler.java:87)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: at cpw.mods.fml.common.FMLCommonHandler.<clinit>(FMLCommonHandler.java:77)
[10:47:35] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStreamrintln:748]: ... 5 more


Et voila, c'est bloqué. Une suggestion ?

Merci.