I've heard of that happening before. I'm not sure why b/c I don't have experience with audio books. iTunes cannot recognise all mp3 audio formats. Ogg Vorbis for example, which is why I have a few mp3 apps such as Audion which does recognise that format. If you have that program then try it out on it. It's quite a popular program despite iTunes. It has more encoding options such as lame than iTunes. For lame for iTunes you need to downld a special 3rd party codec. But getting back to the topic try it out on Audion if you can. Audion is one of the few apps that still produces for both OSX & OS9 & it's more than up to date with codecs such as mp3 pro (for what that's worth lol. IMHO) On mac osx I believe Audion is your best bet! You can always convert it from there such as to AIFF. Else try Toast. If Toast can recognise it then it can also convert it.

As far as membership goes, you can get the site to send you a reminder of your password, etc. I had that problem after deleting the cache & cookies of my browser. Learn from ones mistakes.