Build run's into error and fails in Jenkins - jenkins

Question

I am using jenkins for the build but every time i run a build it gives an error and fails?
These are the errors :
FATAL: hudson/tasks/Mailer$UserProperty
java.lang.ClassNotFoundException: hudson.tasks.Mailer$UserProperty
at
jenkins.util.AntClassLoader.findClassInComponents(AntClassLoader.java:1374)
at
jenkins.util.AntClassLoader.findClass(AntClassLoader.java:1327)
at
jenkins.util.AntClassLoader.loadClass(AntClassLoader.java:1080)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
Caused: java.lang.NoClassDefFoundError:
hudson/tasks/Mailer$UserProperty at
org.jenkinsci.plugins.p4.changes.P4ChangeRef.getChangeEntry(P4ChangeRef.java:18)
at
org.jenkinsci.plugins.p4.tasks.CheckoutTask.getChangesFull(CheckoutTask.java:287)
at
org.jenkinsci.plugins.p4.PerforceScm.calculateChanges(PerforceScm.java:535)
at
org.jenkinsci.plugins.p4.PerforceScm.checkout(PerforceScm.java:496)
at hudson.scm.SCM.checkout(SCM.java:504) at
hudson.model.AbstractProject.checkout(AbstractProject.java:1208)
at
hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild.java:574)
at
jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:86)
at
hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:499)
at hudson.model.Run.execute(Run.java:1815) at
hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43) at
hudson.model.ResourceController.execute(ResourceController.java:97)
at hudson.model.Executor.run(Executor.java:429)
Finished: FAILURE

Answer 1

Sounds like an out-of-date plugin/Jenkins install.
I would recommend updating Jenkins if you're on an older version (I'm currently running 2.121.2).
After Jenkins is updated, try updating all of your plugins as well.
From the main Jenkins page, click "Manage Jenkins" and then "Manage Plugins" or just navigate to: http://yourjenkins.install/pluginManager/.
Scroll to the bottom of the page, click the link "All" near the word Select. Then click the big blue Update button.
This will probably resolve the issue, if not, you've got a bigger issue.