Gnome/Nautilus: Can't associate OO document

Hello When I open the Nautilus file manager and click on a *.sxw document, the message "Nautilus has no installed viewer capable of displaying <file>". I associate the file type with soffice but that doesn't work either (it appears to "take" but subsequent double clicks come back with the first message. Does anyone know where I have to drill to make this work? Cheers