Gerald Brittle, author of a 1980 book on the paranormal investigators, claims not only to have had an exclusive deal with Lorraine Warren, but that producers substantially lifted his work.

An interesting take on the "you infringed upon my earlier work argument."  Two parties - Gerald Brittle  and Warner Bros - created work based upon the case files of alleged parapsychologists Lauren and Ed Warren.  Brittle claims his rights were still in effect based upon his authorship of The Demonologist:

Had defendants done a chain-of-title search, Brittle claims, they would have found they needed his — not Lorraine's — permission and support to legally produce their films. Warren and Brittle initially gave their subsidiary motion picture rights to book publisher Prentice Hall, which later transferred them to Brittle with Warren's agreement.

Warners fired back that their work was based upon "historical facts" and not Brittle's book. According to the article this is "a common argument raised during copyright dust-ups involving true life tales." 

But Brittle claims to have an "ace-in-the-hole" because the Warrens work be frank...bullshit.

"Lorraine and Ed Warrens claims of what happened in their Perron Farmhouse Case File, which the Defendants freely and publicly admit their The Conjuring movie was based on, does not at all jive with the real historical facts," Henry writes. "This is a pattern of deceit that is part of a scheme that the Warrens have perpetuated for years ... There are no historical facts of a witch ever existing at the Perron farmhouse, a witch hanging herself, possession, Satanic worship or child sacrifice."

So the made up stories 

Source: Warner Bros. Facing $900 Million Lawsuit Over 'The Conjuring' Franchise | Hollywood Reporter