Of course that meant one failed bulb and two ruined screens later I was almost ready to give up when the third screen came out well. Still, another trouble, some paper stuck to the screen down the bottom. I cleaned this up with gocco cleaner and a paper towel and eventually things started working.
I think what I learnt from this is not to screen back large areas. They work best as 100% colour. This one I printed at 60lpi and 300dpi. I'm not sure if this lower resolution helps as I haven't tried higher.
