Problem to place a picture in clipping mask

I'm trying to place a picture in a rektangular form in Illustrator. I've made the form, made it a path, and then I mark it together with the picture and try to create clipping mask. But every time I get an error saying that the form isn't a path. But it is! "urklippsbana" in swedish is path. What can be wrong? I'm starting to get grey hairs.