Note to self/anybody else it might help: if you have disks with previous dmraid headers (potentially corrupt etc.), you need to remove the dmraid package before grub can find a Windows partition that resides on those disks. This is because the dmraid package is attempting to map the drives to /dev/mapper locations.
Martin Paul Eve
Professor of Literature, Technology and Publishing at Birkbeck, University of LondonEmail Books Twitter Google+ Github Stackoverflow MLA CORE Institutional Repo Hypothes.is ORCID iD