Elastic search cluster throwing error

My Elastic search cluster which was working fine till yesterday suddenly started throwing "failed send ping to" errors.

Full error : [2016-10-05 01:45:29,394][WARN ][discovery.zen.ping.unicast] [Niles Van Roekel] [1] failed send ping to [#zen_unicast_1#][machineName][inet[masterName/192.186.2.1:9300]]
org.elasticsearch.ElasticsearchIllegalStateException: can't add nodes to a stopped transport
at org.elasticsearch.transport.netty.NettyTransport.connectToNode(NettyTransport.java:709)
at org.elasticsearch.transport.netty.NettyTransport.connectToNodeLight(NettyTransport.java:699)
at org.elasticsearch.transport.TransportService.connectToNodeLight(TransportService.java:220)
at org.elasticsearch.discovery.zen.ping.unicast.UnicastZenPing$3.run(UnicastZenPing.java:373)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

Please let me know if anyone is familiar with this error. I havent made any changes at my end

Could it just be that one of your nodes doesn't see other nodes anymore hence pings fail?