native typeface cannot be made

Hi there,

I am trying to add a custom font to my app. However, I keep getting this error message "native typeface cannot be made".

the code I am using is this:

Typeface face = Typeface.CreateFromAsset (Application.Context.Assets, "fonts/kgpartofme.tff");
            buttonA = FindViewById<Button> (Resource.Id.btnLetterA);
            buttonA.SetTypeface (face, TypefaceStyle.Normal);

I have a fonts folder inside my assets that contains the custom font.

Can anyone help me out or point me in the right direction?

Thank for your time!