I kept having this error. I had to take off parts of the article until I was able to import it. I’m not sure if I should just insert spaces everywhere so the system will interpret long words as short ones, I’m just not good enough in japanese yet to find rapidly where the problem is, hehe!
Same thing happened to me when I tried to copy your text. However, I was able to copy approx. a paragraph of it into a private lesson. As a temporary solution, you could do this, save & open, then click on the edit tool & try adding more of the text in increments to your lesson.