[quote=XBoxBoy]you can sell the copyright rights even though you don’t sell the copyright.
[/quote] Um – I hope those are your words and not an attorney’s. . . Anyway – here is the question: If they stop paying, who does the copyright belong to? If you have assigned (sold it), the copyright no longer belongs to you, and your only recourse would be to sue for breach of contract. Generally speaking, you don’t assign without getting the money up front, just as you wouldn’t transfer title on a house without getting the money up front.
Here’s at least one question. Copyrights, to be enforceable, must be registered with the U.S. (for US citizens) Copyright Office. Who do THEY think owns it? Have you filed a document with the Copyright office assigning the ownership of the copyright to someone else?