saving as postscript only saving part of pages document

I am trying to save a 30x40 to postscript before bringing it into distiller to create a pdf with transparency for press printing. This process usually works well, however with this poster, it is only copying part of the image. (If I simply convert to pdf through pages, the entire page is shown, but I know from past experience that I will have transparency issues). Strangely, while the items (text, shapes, images) are selectable, object placement options are not selectable, though object causes wrap is selectable. I am using pages 4.03 and other documents I open have items which are selectable and placement does work. The strange thing is that I have had this same issue before with other posters, and even stranger - the same document will sometimes convert correctly to ps and then not at other times. Any ideas would be greatly appreciated.