OK if anyone out there knows what the problem might be I'd appreciate your thoughts. It's quite clever that it is possible to download and reinstall the OS, but I'd prefer not to have to. Fortunately all files are safe due to careful backup systems. If you don't backup to more than one place then I suggest you think about it. PCs, laptops, Macs and especially hard drives all fail with a remarkable frequency!
Mind back on a PaD proper tomorrow :)