I had this same "not authenticated" stuff on another miner app on dwarfpool.
I guess it's not only claymore's miner, but also the pool.
will try another pool now , if it 's only with drawfpool , better is to tell them , and wait for fix , they did , update today , website was offline all morning (europe)
I think it could even be that dwarf pool op really dislikes the "invalid shares", so it responds with garbage on purpose.