What was Das Ganu's specific problem with the Ishavasya Upanishad, and what was Sai Baba's strange advice?

Chapter 20 explains that Das Ganu was writing a commentary called 'Ishavasya-Bhavartha-Bodhini' to explain the Upanishad in a simple language. Although he translated it word for word, he became stuck on a doubt because he felt he couldn't grasp the 'internal secret' or deep meaning, and his mind found no joy in the work. When he took this doubt to Sai Baba in Shirdi, Baba gave him the curious instruction that the doubt would be resolved by the maidservant at Kaka's house when he returned there.