Thanks for the thoughts, Grazie. Turning off GPU fixed the problem. Obviously I need to look at my card and its drivers as it is getting a bit ancient... 3 years is a long time in Computerworld.
Looking back at my Vegas 12 setting I see GPU was turned off there too... so down to the store I go.
Once again, thanks.
Windows 7 Pro64, i7 CPU, 16GB RAM, SSD boot drive, GTX 570 Graphics, Vegas Pro 12