ava.lang.NoSuchMethodError: mekanism.common.item.ItemJetpack.setTileEntityItemStackRenderer(Lnet/minecraft/client/renderer/tileentity/TileEntityItemStackRenderer;)V
at mekanism.client.ClientProxy.registerItemRenders(ClientProxy.java:386)
at mekanism.common.Mekanism.registerModels(Mekanism.java:306)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_197_Mekanism_registerModels_ModelRegistryEvent.invoke(.dynamic)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
at net.minecraftforge.fml.common.eventhandler.EventBus$1.invoke(EventBus.java:143)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:179)
at net.minecraftforge.fml.client.FMLClientHandler.fireSidedRegistryEvents(FMLClientHandler.java:1095)
at net.minecraftforge.fml.common.FMLCommonHandler.fireSidedRegistryEvents(FMLCommonHandler.java:757)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:604)
at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:270)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:466)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:377)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

or

Error: java.lang.NoSuchMethodError: mekanism.common.item.ItemJetpack.setTileEntityItemStackRenderer(Lnet/minecraft/client/renderer/tileentity/TileEntityItemStackRenderer;)V

1.12 is not supported anymore and you gave so little information that I can't even suggest what the problem might be.

i dont have more information that it.