Exception: Failed to load content type with name 'CategoryData' when working with Geta.EpiCategories plugin

I've been struggling with an exception while I'm trying to import the package to one of the websites -

This has been due to the plugin installed - https://github.com/Geta/EpiCategories

So it's expecting a ContentType named 'CategoryData' which in my case I've two/category - 

 [ContentType]
    public class PressCategory : CategoryData
    {
    }
    [ContentType]
    public class GuestReportingCategory : CategoryData
    {
    }

And the block has a property that basically overrides the default Category of page/block

Any idea what may have happened?