Custom modpack crashing upon game launch

[SolidMercury]

i'm putting together a modpack for me and some friends, i add a few mods then check if there any problems, well there are and i cant seem to fix it... this is the crash message 

The game crashed whilst initializing game Error: java.lang.IllegalAccessError: class com.laidbacksloth.brightnessslider.BetterSlider cannot access its superinterface net.minecraft.client.OptionInstance$SliderableValueSet (com.laidbacksloth.brightnessslider.BetterSlider is in module [email protected] of loader 'TRANSFORMER' @713a35c5; net.minecraft.client.OptionInstance$SliderableValueSet is in module [email protected] of loader 'TRANSFORMER' @713a35c5)

 

there is also a much longer message in the full crash report

[warjort]

Quote

com.laidbacksloth.brightnessslider.BetterSlider

Issue with whatever mod provides that class.

If you didn't truncate error messages, we could probably tell you the jar name of the mod that is causing the problem.

[SolidMercury]

laidbacksloth is a mod maker, the only mod i had from him causing the issue and i removed it and solved it, thank you!