What was the specific problem Das Ganu faced while writing his commentary on the Ishavasya Upanishad, as detailed in Chapter 20?

In Chapter 20, we learn about the challenge faced by Das Ganu. He had started writing a commentary called 'Ishavasya-Bhavartha-Bodhini' to explain the meaning of the Ishavasya Upanishad in simple language for those who did not know Sanskrit. Although he had translated the text word for word, he found no joy because he could not grasp its internal secret and deep meaning. When he brought this doubt to Sai Baba, the Satguru cryptically told him the resolution would come from a maidservant at Kaka’s house.