I am implementing simple form with input fields and file upload. I went over tutorial: http://grails.org/Simple+Avatar+Uploader and documentation: http://grails.org/doc/2.0.
By the type in your stack trace, the Spring Security @Secured annotation is wrapping your request in a SecurityContextHolderAwareRequestWrapper. You need to get at the MultipartHttpServletRequest to call getFile I believe.
Also, in your debug Here are params statement, are you seeing the itemImage? If so, I actually think it might be this easy.
def file = params.itemImage
UPDATE: I upvoted the comments. They weren't there when I started typing.