Got this error:
Description: There was a severe problem during mod loading that has caused the game to fail

net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Redstone Flux (redstoneflux)
Caused by: java.lang.RuntimeException:
RedstoneFlux has detected that the following OLD API classes from CoFHLib are being repacked!
cofh.api.energy.ItemEnergyContainer, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.EnergyStorage, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.TileEnergyHandler, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.IEnergyConnection, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.IEnergyProvider, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.IEnergyHandler, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.IEnergyStorage, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.IEnergyContainerItem, loaded from: sparkshammers-1.12-1.6.6.jar
cofh.api.energy.IEnergyReceiver, loaded from: sparkshammers-1.12-1.6.6.jar

To prevent this crash, add "-Dcofh.rf.crashOnOldAPI=false" to your command line arguments.

at cofh.redstoneflux.internal.OldAPIChecker.check(OldAPIChecker.java:64)
at cofh.redstoneflux.RedstoneFlux.preInit(RedstoneFlux.java:25)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

...

Representing CoFH here, You need to update and depend on the new API not repack it, https://minecraft.curseforge.com/projects/redstone-flux For more info.

The -Dcofh.rf.crashOnOldAPI=false is to provide users with a way to still play the game with the old api present but it will be functionally incompatible with the actual released RF.

Thanks for all the help guys, I've fixed this in the commit 28afd42