When did the Church start calling Mary Magdalene a Prostiture? Dr. Rainy

It is true that traditional Roman Catholic teaching confuses Mary Magdalene with the 'woman who was a sinner' in Luke 7.37. Dr. Langdon dates this from the fourth century, and claims that 'the Vatican' was responsible. Never mind the popes lived at the Lateran in those days, of course.
I'd agree with him, on the whole. But what Dr. Langdon does not seem to realise is that there never was a time when the whole Church regarded the Pope as head. The Eastern Orthodox Churches have always considered themselves equal to the Western Catholc Church, and the Patriarchs of Antioch, Constantinople, Alexandria and Jerusalem were of equal authority to the Church of Rome.
Eastern Greek fathers never confused Mary Magdalene and the 'Woman who was a sinner'. But in the West Pope Gregory I (Gregory the Great) did confuse the two. In fact, he confused Mary Magdalene, the 'Woman who was a sinner' and Mary of Bethany, the sister of Lazarus. He did this in a sermon in 591. This confusion of the three was common in the West until the Reformation, when Protestant exegetes actually looked at the original text of Scripture, they realised that Gregory had been hoplessly confused, and they distinguished the three.
Preaching on Mary Magdalene, I have noted first of all that she was not a prostitute, but a rich woman who was possessed by 'seven demons'. She must have been wealthy because she 'ministered' to Christ of 'her substance'.