here is the source , can someone help me figure it out?
#355] java.lang.NoClassDefFoundError: net/minecraftforge/fml/relauncher/IFMLLoadingPlugin
[B#355] at java.lang.ClassLoader.defineClass1(Native Method) ~[?:1.7.0_80]
[B#355] at java.lang.ClassLoader.defineClass(ClassLoader.java:800) ~[?:1.7.0_80]
[B#355] at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) ~[?:1.7.0_80]
[B#355] at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) ~[?:1.7.0_80]
[B#355] at java.net.URLClassLoader.access$100(URLClassLoader.java:71) ~[?:1.7.0_80]
[B#355] at java.net.URLClassLoader$1.run(URLClassLoader.java:361) ~[?:1.7.0_80]
[B#355] at java.net.URLClassLoader$1.run(URLClassLoader.java:355) ~[?:1.7.0_80]
[B#355] at java.security.AccessController.doPrivileged(Native Method) ~[?:1.7.0_80]
[B#355] at java.net.URLClassLoader.findClass(URLClassLoader.java:354) ~[?:1.7.0_80]
[B#355] at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:117) ~[launchwrapper-1.12.jar:?]
[B#355] at java.lang.ClassLoader.loadClass(ClassLoader.java:425) ~[?:1.7.0_80]
[B#355] at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ~[?:1.7.0_80]
[B#355] at java.lang.Class.forName0(Native Method) ~[?:1.7.0_80]
[B#355] at java.lang.Class.forName(Class.java:278) ~[?:1.7.0_80]
[B#355] at cpw.mods.fml.relauncher.CoreModManager.loadCoreMod(CoreModManager.java:460) ~[modpack.jar:?]
[B#355] at cpw.mods.fml.relauncher.CoreModManager.discoverCoreMods(CoreModManager.java:389) ~[modpack.jar:?]
[B#355] at cpw.mods.fml.relauncher.CoreModManager.handleLaunch(CoreModManager.java:221) ~[modpack.jar:?]
[B#355] at cpw.mods.fml.relauncher.FMLLaunchHandler.setupHome(FMLLaunchHandler.java:90) [modpack.jar:?]
[B#355] at cpw.mods.fml.relauncher.FMLLaunchHandler.setupClient(FMLLaunchHandler.java:67) [modpack.jar:?]
[B#355] at cpw.mods.fml.relauncher.FMLLaunchHandler.configureForClientLaunch(FMLLaunchHandler.java:34) [modpack.jar:?]
[B#355] at cpw.mods.fml.common.launcher.FMLTweaker.injectIntoClassLoader(FMLTweaker.java:126) [modpack.jar:?]
[B#355] at net.minecraft.launchwrapper.Launch.launch(Launch.java:115) [launchwrapper-1.12.jar:?]
[B#355] at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
[B#355] Caused by: java.lang.ClassNotFoundException: net.minecraftforge.fml.relauncher.IFMLLoadingPlugin
[B#355] at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191) ~[launchwrapper-1.12.jar:?]
[B#355] at java.lang.ClassLoader.loadClass(ClassLoader.java:425) ~[?:1.7.0_80]
[B#355] at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ~[?:1.7.0_80]
[B#355] ... 23 more
[B#355] Caused by: java.lang.NullPointerException
[B#355] at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182) ~[launchwrapper-1.12.jar:?]
[B#355] at java.lang.ClassLoader.loadClass(ClassLoader.java:425) ~[?:1.7.0_80]
[B#355] at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ~[?:1.7.0_80]
[B#355] ... 23 more
[B#355] Exception in thread "main" [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: java.lang.NoClassDefFoundError: net/minecraftforge/fml/relauncher/IFMLLoadingPlugin
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.defineClass1(Native Method)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.security.AccessController.doPrivileged(Native Method)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:117)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.Class.forName0(Native Method)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.Class.forName(Class.java:278)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.relauncher.CoreModManager.loadCoreMod(CoreModManager.java:460)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.relauncher.CoreModManager.discoverCoreMods(CoreModManager.java:389)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.relauncher.CoreModManager.handleLaunch(CoreModManager.java:221)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.relauncher.FMLLaunchHandler.setupHome(FMLLaunchHandler.java:90)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.relauncher.FMLLaunchHandler.setupClient(FMLLaunchHandler.java:67)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.relauncher.FMLLaunchHandler.configureForClientLaunch(FMLLaunchHandler.java:34)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.common.launcher.FMLTweaker.injectIntoClassLoader(FMLTweaker.java:126)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.Launch.launch(Launch.java:115)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: Caused by: java.lang.ClassNotFoundException: net.minecraftforge.fml.relauncher.IFMLLoadingPlugin
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: ... 23 more
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: Caused by: java.lang.NullPointerException
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
[B#355] [08:04:57] [main/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: ... 25 more