iTunes won't allow me to change media type on multiple files grouped

MP3 files have to be imported into iTunes manually, as music, and it often won't allow me to change the media type to audiobook on multiple files at the same time, forcing it to be done one file at a time. Since audiobooks are often made up of as many as 200 files, it can be a time consuming task.

After importing an audiobook, the next step is to change the media type to "audiobooks". I highlight all of the files, click on "get info", and go to "options", but the only choice offered is music. Alternately, i get a response that says I can't make the change on multiple items because the selected files are different media types. Problem is, they're not.

About half the time, I can do it without a problem; sometimes it doesn't change all the files, and too often it won't change them at all.