Who knows could be something to do with that. I tried removing my google account from my Nexus and re-adding it - I then tried to buy an app which I previously hadn't attempted to buy, and that worked, but then going back to a different app that had failed before, no joy!
However, I've not just bought another app (spending a small fortune here!!) through the Online store, and that has worked.
I think it may be one particular app that is causing the problems - screenslider by REDFLY...
Going to stop testing app purchases, as I've now spent about