Hi - thanks for the replies. Sorry for the delay in my update.
Shortly after having this problem I had hardware problems with my PC - my PC's memory failed and one of my hard disk drives might also be faulty.
I am almost certain that the faulty drive was redundant (empty) at the time - whether or not this would cause general problems with the drive controller I'm not sure.
I have replaced both components and installed Windows/DOpus on the new drive which is running fine and re-installed DOpus on the old Windows drive (at the moment I have two bootable Windows builds on my PC).
Both installations appear to be running fine and I've had no re-occurrence of the problem so far, but if I do, I'll let you know, hopefully with more detailed information.