Hi Smadell.
Many thanks for the answer, I was fully expecting the operator error answer ;-). Having read some of your other posts I experimented further by creating my own luminosity selections and creating a mask from then. This, as you said produced a grey scale image, the bit I find intriguing is what do the marching ants represent? I'm guessing it represents a threshold. Anyway to cut a long story short, I'd seen some youtube from Jimmy McCintire (spelling?) using photoshop with luminosity masks where he was painting into a selection to further blend the result, this is what I was attempting. Mostly I'm happy with the blend ranges result, but the image I was adjusting wasn't playing ball due to the tonal range, so I thought I'd try something different. More experimenting required I think.
Once again many thanks for the quick, informative, response.