I got an email from D2D asking me to re-download the file making sure I used their downloader and deletig all instanes of the download/installed game off my system. I did so and it now works fine. Corrupt file at either the D2D end or corrupted in the DL process maybe - but interesting that I wasn't the only one. DON'T download the zip file by right-click download, install the D2D downloader and get the file with it (I had to use IE for this, not Firefox) as it auto-extracts the zip as part of the DL process.
I had a quiet giggle over one or two other emails that I got saying that my video card/laptop (6 months old) was too old for the game etc... because the demo and original game play out just fine as do games that have higher resource needs

But I guess you have to exhaust every avenue.