OK I figured it out for anyone who is having the same issue. For proper use of the Meph it appears you need the settings to be 2d, Meph color, Masterwork Font, Meph Tileset, Truetype Font ON, and Creature Sprites ON.
For Proper use of ASCII you need to have "text will be text", Vanilla Color, Default Font, ASCII Tileset, Truetype Font OFF, Creature Sprites OFF. Text will be text font should be ASCII font or perhaps Gemset.
With these combos I haven't gotten any errors. I'm not sure why these proper configurations are not suggested in the instructions, it makes it seem like any combo should work for any set, which apparently is not the case.