Crash when i try to start minecraft

minecraft crashes when i try to start it

I’m having trouble starting up Minecraft with the modpack. it works fine usually, but if i am ever disconnected from the internet or on airplane mode and try to run Minecraft with the Ardacraft modpack to just use it in singleplayer it crashes on the start up. After that no matter if i’m on internet or not it continues to crash when i try to run it. this is what appears on my screen:

[16:04:58] [main/INFO]: Loading tweak class name net.minecraftforge.fml.common.launcher.FMLTweaker
[16:04:58] [main/ERROR]: Unable to launch
java.lang.ClassNotFoundException: net.minecraftforge.fml.common.launcher.FMLTweaker
at$ ~[?:1.8.0_25]
at$ ~[?:1.8.0_25]
at Method) ~[?:1.8.0_25]
at ~[?:1.8.0_25]
at java.lang.ClassLoader.loadClass( ~[?:1.8.0_25]
at sun.misc.Launcher$AppClassLoader.loadClass( ~[?:1.8.0_25]
at java.lang.ClassLoader.loadClass( ~[?:1.8.0_25]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass( ~[launchwrapper-1.12.jar:?]
at java.lang.ClassLoader.loadClass( ~[?:1.8.0_25]
at java.lang.ClassLoader.loadClass( ~[?:1.8.0_25]
at java.lang.Class.forName0(Native Method) ~[?:1.8.0_25]
at java.lang.Class.forName( ~[?:1.8.0_25]
at net.minecraft.launchwrapper.Launch.launch( [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main( [launchwrapper-1.12.jar:?]
Java HotSpot™ 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release

the only way I can make it work is if I completely delete and re-install the modpack.

use the support ticket format please