There seems to be an issue with some cpuminer/2.3.2 (i assume that's AMiner) users massively submitting invalid shares to the pool (a few dozen per second to be exact).
Though i tested AMiner with no issues, this may still be an obscure stratum difficulty glitch, if you experience this and you are sure your miner and network are working properly, debug logs would be appreciated.
Alternatively, you may try the latest cpuminer-opt or try increasing difficulty via password (-p c=ANI,d=0.1 for example).