BaseMeshEffect could not be found

I'm getting an error CS0246 saying the file 'BaseMeshEffect' could not be found. But the same project in my colleagues computers work fine. Where can I find this file?

Assets/_UI/Packages/Gamestrap UI/Effects/ShadowEffect.cs(11,33): error CS0246: The type or namespace name `BaseMeshEffect' could not be found. Are you missing a using directive or an assembly reference?

Thanks