Tauhid Asma' wa sifat

I am just registering my confusion after following the tazkirah last night (Tuesday, 29th June 2010) on the above topic by our beloved Ustaz Dr. Mustapha Omar. He strongly emphasised that when doing a do'a, one should only "menyeru" any one of God's names that are mentioned in the Al-Quran or Hadith (i.e. the 99 names of Allah), such as "Ya Rahman", "Ya Rahim" (these are my examples) and not any other names. However when asked about the popular zikir "Ya Amaanal Kho ifin........." which at one time was often recited by by the jamaah in responding to the imam's do'a, our ustaz said it was ok. But this definitely is not one of the Asmaa Allahul Husna! Thus my confusion. My understanding is, Ustaz was saying we should only "menyeru" one of the Asmaa Allahul Husna, but in the same vein he was saying it is ok to "seru" other names. I am sorry to say but I feel our ustaz is contradicting himself.

I will be writing regarding visits to places of historical significance, in particular the Pyramids, later insyaAllah. Also I would like to comment on Ustaz's comments on alternative medicine as practised by quite a number of Ustaz now.