We met an issue about Github plugin failed to checkout pull request from github.com

The step log shows:

13:42:10,470 ERROR - Step 'master>Compile Pull Request>Checkout>checkout source' is failed.
java.lang.RuntimeException: org.eclipse.egit.github.core.client.RequestException: Validation Failed (422): This SHA and context has reached the maximum number of statuses.
at com.google.common.base.Throwables.propagate(Throwables.java:160)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository.onBuildStart(GitHubRepository.java:76)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository.checkoutByRevision(GitHubRepository.java:66)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641.CGLIB$checkoutByRevision$25( )
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641$$FastClassByCGLIB$$1386bcd6.invoke( )
at net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:215)
at com.pmease.quickbuild.DefaultScriptEngine$Interpolator.intercept(DefaultScriptEngine.java:261)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641.checkoutByRevision( )
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository.checkoutByRevision(GitHubRepository.java:49)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641.CGLIB$checkoutByRevision$26( )
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641$$FastClassByCGLIB$$1386bcd6.invoke( )
at net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:215)
at com.pmease.quickbuild.DefaultScriptEngine$Interpolator.intercept(DefaultScriptEngine.java:261)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641.checkoutByRevision( )
at com.pmease.quickbuild.repositorysupport.Repository.checkout(Repository.java:228)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641.CGLIB$checkout$108( )
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641$$FastClassByCGLIB$$1386bcd6.invoke( )
at net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:215)
at com.pmease.quickbuild.DefaultScriptEngine$Interpolator.intercept(DefaultScriptEngine.java:261)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository$$EnhancerByCGLIB$$d6882641.checkout( )
at com.pmease.quickbuild.repositorysupport.CheckoutStep.run(CheckoutStep.java:71)
at com.pmease.quickbuild.repositorysupport.CheckoutStep$$EnhancerByCGLIB$$4d7f1f66.CGLIB$run$2( )
at com.pmease.quickbuild.repositorysupport.CheckoutStep$$EnhancerByCGLIB$$4d7f1f66$$FastClassByCGLIB$$c39c1c48.invoke( )
at net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:215)
at com.pmease.quickbuild.DefaultScriptEngine$Interpolator.intercept(DefaultScriptEngine.java:261)
at com.pmease.quickbuild.repositorysupport.CheckoutStep$$EnhancerByCGLIB$$4d7f1f66.run( )
at com.pmease.quickbuild.stepsupport.Step.doExecute(Step.java:654)
at com.pmease.quickbuild.stepsupport.Step.execute(Step.java:568)
at com.pmease.quickbuild.stepsupport.StepExecutionJob.executeStepAwareJob(StepExecutionJob.java:31)
at com.pmease.quickbuild.stepsupport.StepAwareJob.executeBuildAwareJob(StepAwareJob.java:56)
at com.pmease.quickbuild.BuildAwareJob.execute(BuildAwareJob.java:77)
at com.pmease.quickbuild.grid.GridJob.run(GridJob.java:129)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.eclipse.egit.github.core.client.RequestException: Validation Failed (422): This SHA and context has reached the maximum number of statuses.
at org.eclipse.egit.github.core.client.GitHubClient.createException(GitHubClient.java:583)
at org.eclipse.egit.github.core.client.GitHubClient.sendJson(GitHubClient.java:674)
at org.eclipse.egit.github.core.client.GitHubClient.post(GitHubClient.java:788)
at org.eclipse.egit.github.core.service.CommitService.createStatus(CommitService.java:428)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository.updateCommitStatus(GitHubRepository.java:205)
at com.pmease.quickbuild.plugin.scm.github.GitHubRepository.onBuildStart(GitHubRepository.java:73)

Can I know what this means and how to fix/avoid ?
What is the maximum number of statuses ?

Thanks,
Zachary