Suddenly can't run TestNG tests from ant ([testng] Caused by: java.lang.ClassNotFoundException: com.beust.jcommander.ParameterException)

I am using ant and TestNG 6.1.1, and I had my tests working just fine yesterday. Today when I try to run the tests I get a NoClassDefFoundError involving com/beust/jcommander/ParamException. Here is the output:

[copy] Copying 1 file to /Users/djohnson/src/webapp/components/build/tmp
[testng] Exception in thread "main" java.lang.NoClassDefFoundError: com/beust/jcommander/ParameterException
[testng] Caused by: java.lang.ClassNotFoundException: com.beust.jcommander.ParameterException
[testng]    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
[testng]    at java.security.AccessController.doPrivileged(Native Method)
[testng]    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
[testng]    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
[testng]    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
[testng]    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
[testng] The tests failed.

Here is the .xml file I'm using:

<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd" >
<suite name="Single Method Suite">
  <test name="Single Method Test">
    <classes>
      <class name="DhcpTest">
        <methods>
          <exclude name=".*" />
          <include name="setGetEnabledTest" />
        </methods>
      </class>
    </classes>
  </test>
</suite>

I've also specified the complete path for the class with no luck. I've checked the classpath and everything seems fine, does anyone have any ideas on this?

If you're using ant, JCommander should be inside testng.jar, so I'm thinking your testng.jar file might be corrupt.

If your using Maven try adding this to your pom.xml

<dependency>
  <groupId>com.beust</groupId>
  <artifactId>jcommander</artifactId>
  <version>1.30</version>
</dependency>

jcommander.jar (e.g. jcommander-1.29.jar) should be present on fileset directory which is mentioned at build.xml

You can download it from: http://mvnrepository.com/artifact/com.beust/jcommander/1.27

OR,

JCommander should be inside testng.jar during using ant. Your testng.jar file might be corrupted, so please replace old testng.jar by new one.