Minecraft CurseForge

I'm sorry to bother anyone but i really need help every mod pack i try just crashes it goes to the minecraft launcher and then after it the loading bar makes it to the last little bit it tells me it couldn't start up here is the exact text that appears 

[01:12:27] [main/INFO]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[01:12:27] [main/ERROR]: Unable to launch
java.lang.ClassNotFoundException: cpw.mods.fml.common.launcher.FMLTweaker
at java.net.URLClassLoader$1.run(URLClassLoader.java:372) ~[?:1.8.0_25]
at java.net.URLClassLoader$1.run(URLClassLoader.java:361) ~[?:1.8.0_25]
at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_25]
at java.net.URLClassLoader.findClass(URLClassLoader.java:360) ~[?:1.8.0_25]
at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_25]
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) ~[?:1.8.0_25]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_25]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:106) ~[launchwrapper-1.12.jar:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_25]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_25]
at java.lang.Class.forName0(Native Method) ~[?:1.8.0_25]
at java.lang.Class.forName(Class.java:344) ~[?:1.8.0_25]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:98) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option PermSize=256m; support was removed in 8.0

any help at all would be appreciated thank you

Try reinstalling the game by backing up important game files (ex: worlds) and delete everything in your .minecraft folder reinstall and do everything again and then see if it works. I did that before when a mod pack I was using didnt work and now it does. If that doesnt do anything make sure your on the right version of forge