Federico Fellini's La Dolce Vita From Wikipedia
Two recent cases underline the importance of being able to prove a written chain of title if you would like to bring a claim for copyright infringement. If you wish to sue a gay pornographer for making a version of your film (Michael Lucas' La Dolce Vita). In both International Media Films, Inc. v. Lucas Entertainment, Inc., 2010 WL 125358 (March 31, 2010) and American Plastic Equipment, Inc. v. Toytrackerz, LLC, 2010 WL 1284471 (March 31, 2010), each copyright infringement plaintiff could not prove a chain of title showing ownership of the copyrighted work.
17 U.S.C. 204(a) says that transfers of exclusive rights need to be in writing. There is an exception for non-exclusive writings and transfers "by operation of law".
The Fellini plaintiff had documents that looked liked they had been faked in Lichtenstein.
It looks like the American Plastic Equipment plaintiff did actually own the copyright, but didn't bother searching bankruptcy court records prior to judgment and waited until 60 days after judgment was entered against it to make a motion with "newly discovered evidence".
That is why it is so important to do research before bringing a lawsuit. Document your chain of title and register your ownership with the Copyright Office.