Java run SSHD Server Error - No class def found

I am currently running a Java Mina SSHD server.
I had my server running fine with sshd-core-0.14.0 but my virus scanner was flagging weak ciphers leaving me no choice but to upgrade to version 2.5.1. I have tried simply replacing the .jar files and changing the classpath vars to the new versions but get the following error.

Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: org.apache.sshd.commo
n.KeyPairProvider
        at java.lang.J9VMInternals.prepareClassImpl(Native Method)
        at java.lang.J9VMInternals.prepare(J9VMInternals.java:303)
        at java.lang.Class.getMethodHelper(Class.java:1247)
        at java.lang.Class.getMethod(Class.java:1191)
        at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:556
)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:538)
Caused by: java.lang.ClassNotFoundException: org.apache.sshd.common.KeyPairProvi
der
        at java.net.URLClassLoader.findClass(URLClassLoader.java:610)
        at java.lang.ClassLoader.loadClassHelper(ClassLoader.java:944)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:889)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:872)
        ... 6 more

The code that starts my java based SSHD is here:

import org.apache.sshd.SshServer;
import org.apache.sshd.server.keyprovider.SimpleGeneratorHostKeyProvider;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class WinSSHServer {
	public WinSSHServer(Properties props) throws IOException {
		final SshServer sshd = SshServer.setUpDefaultServer();

		sshd.getProperties().put(SshServer.IDLE_TIMEOUT, String.valueOf(sessionTimeoutMSec));
		sshd.setPort(22);
		sshd.setKeyPairProvider(new SimpleGeneratorHostKeyProvider(props.getProperty("hostkey")));
		sshd.setCommandFactory(new WinCmdExeCommandFactory());

		final PuTTYPublicKeyAuthenticator pka = new PuTTYPublicKeyAuthenticator();
		addPublicKeysFromProps(pka, props);
		sshd.setPublickeyAuthenticator(pka);

		sshd.start();
	}

Probably there is a huge difference between version 0.14.0 and 2.5.1 That class may not really exist in 2.5.1 Therefore

1. try to compile your project with the new version first (instead of changing the jars in the lib)
2. change your code accordingly to comply with the new version

I searched in a maven repository index site and found a JAR that contains the same class. However, there is a change in the path that you likely have to configure on your end.

I did this using a zip utility (7zip) to search through the packages to find the class name in question and its fully-qualified class path. There are other ways to do this as well.

https://mvnrepository.com/artifact/org.apache.sshd/sshd-common/2.5.1

The path given in the exception stack by original poster is org.apache.sshd.common.KeyPairProvider however in this package it appears to be org.apache.sshd.common.keyprovider.KeyPairProvider (note the keyprovider that was added).

Steps to troubleshoot:

1. Confirm you have the class present in one of your jars
2. If the fully qualified class name for KeyPairProvider did change as mentioned above then update references to the new fully qualified class name