Thank you for your reply.
Actually my computer is a new build.
I did think of the graphics card, but the AMD Radeon HD7700has the latest drivers.
I always shut down then re-boot and only use restart when installing software.
I have since discovered that some projects seem to mix-down fine, but I have not isolated the different factors involved.
The weird thing is that when a faulty mix-down and crash occurs a file is left in the mixdown folder. It will not play in Media Player. If I delete it the next time I do a mixdown the same thing happens. If I don’t delete it at the beginning of the mix-down the window asking if I want to overwrite or rename the file comes up and when I select Overwrite the mixdown takes place but Cubase crashes at the end when the mix-down window reappears.
I have sent some crash dumps to support. However I am still awaiting a query about Padshop Pro which was about 4 weeks ago. So I’m not holding my breath.