• Check if the host name is correct.
  

• Check if the port number given is the JMX port number. We need JMX port number and not HBase DB port number for monitoring. The JMX port number will be available in hbase-env.sh file.
  

• if hbase is running in authenticated modes, then enable "Is Authentication required", and give correct username and password.
  

• Check if below lines are uncommented in hbase-env.sh
  

HBASE_JMX_BASE

HBASE_MASTER_OPTS

HBASE_REGIONSERVER_OPTS