Question: I am in a lot of unhappiness and confusion in my life. I also feel that I am under the influnce of black magic. I heard and read in Srila Prabhupada's books that the maha mantra is the solution for everyhting. However I also read (please correct me if i am wrong) that one must chant without offense to get the proper effect. Could I chant the Gaura - nama instead because there is no consideration of offense?
Answer: Chanting the maha mantra is always auspicious. Gradually it will clean our heart from all bad influences and nourish the longing of the soul. This transcendental sound vibration has so much power and mercy that it will always and under any circumstances have some positive effect.
However, the highest effect of the mantra can only be achieved when it is received from a spiritual master. Only then it is possible to chant the Holy Names of the Lord without offenses. Our faith and dedication to the spiritual master will help us to overcome all offenses.
In our sampradaya I do not know of any guru who initiates disciples exclusively in the names of Sri Chaitanya Mahaprabhu and Sri Nityananda prabhu. The names of Lord Chaitanya and Lord Nityananda are part of the life of a Vaishnava and surely will give mercy and spiritual insights to a person who meditates upon them and renders service to Gurudeva; but excluding the maha mantra certainly does not come in the line of Srila Bhaktisiddhanta Sarasvati Thakur Prabhupada.
Once Srila Bhaktivijnana Bharati Maharaja responded to the same question that it is all a question of the faith in Sri Gurudeva. If we have faith in Sir Gurudeva no desire will come up to change his instructions.
As you wrote in the question, Srila Prabhupada said that the maha mantra is the solution for everything. If we accept these instructions of our eternal wellwisher, there won't be any doubt about what is to be done.