Failed to get a session to MySQL cluster (no replies)

I setup a 3 node mysql cluster env (one management node and two data nodes).
But I got following error when trying to connect to the cluster with ClusterJ

Caused by com.mysql.clusterj.ClusterJDatastoreException:Datastore exception on connectString '10.247.101.183:1186' nodeId 0; Return code: -1 error code: 1,101 message: Error: Could not alloc node id at 10.247.101.183 port 1186: No free node id found for mysqld(API)..
at com.mysql.clusterj.core.SessionFactoryImpl.createClusterConnection(SessionFactoryImpl.java:252)
at com.mysql.clusterj.core.SessionFactoryImpl.createClusterConnectionPool(SessionFactoryImpl.java:226)

My env looks heathly and here is the output of the 'show' of ndb_mgm:
ndb_mgm> show
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=2 @10.247.101.182 (mysql-5.6.17 ndb-7.3.5, Nodegroup: 0, *)
id=3 @10.247.101.181 (mysql-5.6.17 ndb-7.3.5, Nodegroup: 0)

[ndb_mgmd(MGM)] 1 node(s)
id=1 @10.247.101.183 (mysql-5.6.17 ndb-7.3.5)

[mysqld(API)] 3 node(s)
id=4 @10.247.101.181 (mysql-5.6.17 ndb-7.3.5)
id=5 @10.247.101.182 (mysql-5.6.17 ndb-7.3.5)
id=6 (not connected, accepting connect from 10.247.101.182)

Does anyone know why I get this error and how to resolve it?

Thanks