Scripting problem

Hi I’ve been getting this error code here:
Assets/Standard Assets/Effects/ImageEffects/Scripts/Antialiasing.cs(20,18): error CS0060: Inconsistent accessibility: base class UnityStandardAssets.ImageEffects.PostEffectsBase' is less accessible than class UnityStandardAssets.ImageEffects.Antialiasing’

How can i fix it?

I would suggest reinstalling Unity and the Standard Assets.