This error is returned by the "remove mdisk" rmmdisk command when issued against an MDisk that is backing an image-mode volume on a platform that does not support migration for image-mode volumes.
If the image-mode volume is not required then use rmvdisk to delete the volume. This deletes the MDisk as well. If the user wants to migrate the image-mode volume's data to internal storage, do that using Volume Mirroring and then delete the image-mode volume copy.