I am working on a research project about The Lord of the Rings and my English teacher mentioned some sort of publishing error when the books were being sent to the US for publishing. She has further hinted that it wasn't the copyright/lawsuit issues that it also encountered. Does anyone know anything about this?
It's hard to know exactly what your teacher is referring to. However, recent editions of LoTR include at the beginning a "Note on the Text" written by Douglas A. Anderson, which talks about the history of the revisions made in different editions, and in particular mentions the changes that happened when it was republished in the US.
In 1965, stemming from what then appeared to be copyright problems in the United States, an American paperback firm published an unauthorized and non-royalty-paying edition of The Lord of the Rings. [...]
Tolkien set to work on his first revision of the text so that a newly revised and authorized edition could successfully compete on the American market. This first revision of the text was published in America in paperback by Ballantine Books, under licence from Houghton Mifflin, in October 1965. In addition to revisions within the text itself, Tolkien replaced his original foreword with a new one. [...]
[...] Soon after this he sent a small number of further revisions to Ballantine for the appendicies, including the now well-known addition of 'Estella Bolger' as wife of Meriadoc in the family trees in Appendix C. Most of these revisions [...] somehow never made it into the main sequence of revision in the three-volume British hardcover edition.