Hmm, you could try remaking it. It's strange, especially if it worked on the desktop. I've bought & converted 52 books since I got my Reader without problems. Is this a regular fiction book? Is there anything special/unusual about the book that could be causing problems?
You might want to dig through this thread & see if anyone else has had similar issues...
https://www.mobileread.com/forums/showthread.php?t=11618