Dear Rich: I have a question. Before our divorce, my ex-husband copyright registered an unpublished song he wrote naming me as the sole "copyright claimant". If he publishes or records the song for sale without my consent, can I file a copyright infringement claim against him even though he is the original author? I'm so glad you asked. The short answer to your question is, "Maybe." [BTW, the Dear Rich staff is sorry to hear about your marital woes (even though the subject of divorce has made for some lucrative hit songs and parodies).]
Our first question is whether there is a written document that evidences the transfer between you and your ex-hubby -- any document, note or memorandum establishing the arrangement and signed by your ex. That's required under Section 204 of the Copyright Act. One case (involving vampire-novel author Anne Rice) indicates that the document needs to express the terms of the transfer -- that is, how much each party gets for the transfer -- so it can serve as a guidepost for resolving disputes.
If you don't have this written document, you may have a hard time asserting your rights. Assuming you can satisfy this requirement and you are the sole copyright claimant, then you would control all rights under copyright law. You could prevent your ex from recording and releasing the song. But if you're just doing it to be spiteful -- that is, without a good business reason -- your ex may have an argument that you're acting in bad faith under the terms of the written agreement and that could cause problems in a court battle.
Another issue to consider is how the copyright was treated in the divorce proceedings. Your husband may have a claim to some portion of it under the ultimate property division. (This Nolopedia article may help). Since all of this may seem much more complicated than you originally expected, and since the Dear Rich staff prefers that everybody gets along (and that you avoid legal fees), you may want to draft a written statement with your ex -- assuming you're still on speaking terms -- that addresses these issues, provides for a financial payment in the event the song is a hit, and allows you to retain copyright ownership.