I wouldn't say an 'Inability' because they have shown against Wales that they can, especially through that disallowed try - which should have been a try perhaps one of the best tries for a long time in fact. (Wales would have still won, before anyone suggests otherwise). I think it's down to the players though, they lack confidence, my thoughts are they panick when in space which can be normal, and this makes them make a hash of it. If they simply sorted this out, they would be up there for the 6N each year, and beyond.
As for saying it's due to Robinson, because England were the same, i disagree. England are not made of the most talented, and flashy of players so again its down to those previous players not Robinson. I hope i don't speak to soon, but follow Wales' coach example, everyone wanted him out 12 months ago due to poor results, pretty much the same as with Scotland now. However faith (I hope) will result in some success for years to come, although we have not won anything yet and it's going to be one hell of a game tonight or this afternoon your time.
Scotland just need some luck. That is all.