I was trying out the EPUB export of VoodooPad and figured out I had to make a cover page in the tool as well as a collection. I then filled out the metadata including author information (David Green email@example.com) and then saved with an .epub extension.
Things ran fine but when I moved it over to the iPad as an iBook file, I was told it was an invalid format. Alas, googling did not help me (it has to happen every once in a while).
After a goodly bit of exploring, the problem was the e-mail address in angle brackets as part of the author information. I removed them and things were good to go.