What is the truth on this topic ? A cursory Google search only turned up Protestant links that are anti-Catholic in nature, probably not objective in their discussion / conclusions.
The issue here is Pope Gelasius (this decree is also attributed to Pope Damasus) condemned a long list of books as heretical, including one called "the Assumption of holy Mary." The decree doesn't say specifically what is heretical about the books listed. For example, another book in the list is called "the Infancy of the Savior." Obviously the idea that Jesus was an infant is not what made the book problematic, but there must have been some other heretical stuff in the book--same with the book on the Assumption. This decree was later reaffirmed by Pope Hormisdas. Here is the decree in question:
Yes, that link answers the matter, dealing only with the various books, & not impuning the subject.