Aerospike return write errors messages

Hi, We are working on aerospike with 4 nodes, some times to times we get writes errors in the logs ,
this errors occurred from time to time. We are running with jave client.
Any ideas?
Thanks
Dan
Error message:

2017-11-28 14:49:10,589 [event2] ERROR c.c.e.i.s.AerospikeServiceImpl:328 - Failed to put: set=Connection, key=4s5zj_W3np1ypvx3, bins=[2119324289:UDP, 3979419923:5355, 883731747:AAAACLq-qxNujtW9, 2848269545:83.156.11.215:5355 > 215.47.47.108:63878, 383641883:62, 2466433458:1507010355072, 1110363332:United States, 1454624205:1507010354652, 11052611:215.47.47.108, 296141534:4s5zj0PuNCbZ7277, 722829366:CONNECTION_EMBRYONIC, 678740036:true, 1440140576:63878, 2183309026:AAAACHDqamNWIQpY, 2428847886:62, 3038066921:1507010354652, 3147783044:1507010400000, 753536379:OUTGOING, 4248191738:true, 3494711103:4s5zjxCi55eyTiwX, 3849690159:EXTERNAL, 2151136701:4s5zj_W3np1ypvx3, 2440695305:63878], exception=Error Code -7: Node BB9240750DAF312 172.31.53.203 3000 event loop 2 max connections 19 would be exceeded.

Any one can help?