Is it only Z2 that's causing problems? From your description I get the impression you haven't had problems with other albums in the past. Correct?
Unfortunately I can't help much with it's about iTunes. I've been using CopyTrans Manager instead and been very happy with it. If you don't care for automatic syncing and what-have-you Apple wizardry and prefer old-skool drag & drop managing, it's perfect. Well, almost, as you can only copy files back to your computer with its paid version.
http://www.copytrans.net/download.phpScroll down to "CopyTrans Manager" (second down on the left), choose "download zip (advanced users)" - no need for installers or anything IMO. Just extract the zip file and copy the exe on your iPhone and you're set. No need to keep the program on your computer, just plug your iPhone in and run the manager.
And oh, I don't know if it's a feature of the iPhone too, but with the iPod Classic the library had to be set up (i.e. connect with iTunes for one time and transfer at least one song) before it can work.