Studio Coattails! Thank you for this amazing visual novel first of all.
I just bought and downloaded episode 5 (+ updating the base game and the previous parts (2-4) as per your instructions. (Deleted the original install and started from clean).
I had issues getting this game to start properly and I found out the reason why!
For some reason the directory/folder which the game files resides inside CANNOT have a space in it.
So I solved the issue completely by renaming "National Park Girls" to "NationalParkGirls" without spaces.
Now the game runs fine.