Nero won't read some AIF files

Hi All,
It’s the strangest thing. Nero will read my wavs, mp3s and even some AIFs. But it won’t read aif files ripped with iTunes. I’ve checked to see if there are any differences between the two types of files and I can’t see any. Nero 5 just says that the file type is not supported. Nero 6 says that Nero can’t add the file to the compelation and suggests using a plugin. I checked and I have aif.dll installed. Does anyone have any suggestions?