I fixed the problem by myself. But not only that, it even caused lags on my computer whenever I play Minecraft.
The error message I got was this
"Forge Mod Loader has found a problem with your minecraft installation.
The Mod listed below does not want to run Minecraft 1.8
Chisels & Bits (chiselsandbits) wants to run Minecraft [1.12,1.12]
the file 'ForgeModLoader-client-0.blog' contains more information"
After I've downloaded Chisels and bits version 1.8 for Forge 1.8 on my Minecraft Launcher.
How do I fixed this?