Catharism (/ˈkæθərɪzəm/; from the Greek: καθαροί, katharoi, "the pure [ones]") was a heretical Christian dualist movement that thrived in some areas of Southern Europe, particularly northern Italy and southern France, between the 12th and 14th centuries. In 1208, Pope Innocent III attempted to use diplomacy to end Catharism, but in that year, his papal legate Pierre de Castelnau was murdered while returning to Rome. This prompted the Pope into action and resulted in the Albigensian Crusade. The Albigensian Crusade sought to extinguish the movement in the early decades of the thirteenth century but was not entirely successful. When the pope realized the crusade had failed to eliminate the Catharist movement, he launched the Medieval Inquisition to finish the task.
An article giving details of material on the Cathars, and refuting Levitov's case can be found here 
There are various arguments against Levitov's proposition:
- There is no obvious connection between worship of the ancient Egyptian goddess Isis (or the Egyptian pantheon in general) and the medieval Cathars.
- The VM is dated to the first part of the 15th century - long after the Cathars were suppressed.
- The VM appears to have an Italian origin (rather than southern France, where the Cathars were based).
- The VM appears to be a secular rather than a religious text.
Coverage of the Cathars on the web ranges from the academic/reasonable to the fanciful.