spatpat,
You should be able to load you jp2 file within the Image App as well. Simply replace one of the path of one of the image files with the path to your jp2.
Is there an associated world file with your image? Map Suite requires this to correctly place the image on the map.
If you receive an error when loading the image in the Image App, we may want to setup an FTP transfer so that we could take a look at the image file.
ThinkGeo Support