got follow error while tried to connect to an ubuntu 12.04 agent,

[05/02/17 14:24:44] [SSH] Opening SSH connection to jenkins-agent:22. Key exchange was not finished, connection is closed. java.io.IOException: There was a problem while connecting to jenkins-agent:22 at com.trilead.ssh2.Connection.connect(Connection.java:834) at com.trilead.ssh2.Connection.connect(Connection.java:703) at com.trilead.ssh2.Connection.connect(Connection.java:617) at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1265) at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:790) at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:785) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: java.io.IOException: Key exchange was not finished, connection is closed. at com.trilead.ssh2.transport.KexManager.getOrWaitForConnectionInfo(KexManager.java:95) at com.trilead.ssh2.transport.TransportManager.getConnectionInfo(TransportManager.java:237) at com.trilead.ssh2.Connection.connect(Connection.java:786) ... 9 more Caused by: java.io.IOException: Cannot read full block, EOF reached. at com.trilead.ssh2.crypto.cipher.CipherInputStream.getBlock(CipherInputStream.java:81) at com.trilead.ssh2.crypto.cipher.CipherInputStream.read(CipherInputStream.java:108) at com.trilead.ssh2.transport.TransportConnection.receiveMessage(TransportConnection.java:232) at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:706) at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:502) ... 1 more [05/02/17 14:24:44] Launch failed - cleaning up connection [05/02/17 14:24:44] [SSH] Connection closed.