Error executing resource allocate job #3676

We keep seeing this on some of our agent pools and want to know what it means. If the resource pool isn't fully in use at this point, why is quickbuild having trouble trying to allocate a resource for this build to run on?

18:25:34,193 ERROR - Step 'master' is failed.
java.lang.RuntimeException: Error executing step process job.
at com.pmease.quickbuild.stepsupport.StepProcessTask.reduce(StepProcessTask.java:126)
at com.pmease.quickbuild.stepsupport.StepProcessTask.reduce(StepProcessTask.java:19)
at com.pmease.quickbuild.grid.GridTaskFuture.get(GridTaskFuture.java:102)
at com.pmease.quickbuild.grid.GridTaskFuture.get(GridTaskFuture.java:106)
at com.pmease.quickbuild.stepsupport.SequentialStep.triggerChildren(SequentialStep.java:36)
at com.pmease.quickbuild.stepsupport.CompositeStep.run(CompositeStep.java:117)
at com.pmease.quickbuild.stepsupport.Step.execute(Step.java:539)
at com.pmease.quickbuild.stepsupport.StepExecutionJob.executeStepAwareJob(StepExecutionJob.java:30)
at com.pmease.quickbuild.stepsupport.StepAwareJob.executeBuildAwareJob(StepAwareJob.java:45)
at com.pmease.quickbuild.BuildAwareJob.execute(BuildAwareJob.java:60)
at com.pmease.quickbuild.grid.GridJob.run(GridJob.java:106)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.RuntimeException: Error executing resource allocate job.
at com.pmease.quickbuild.resource.ResourceAllocateTask.reduce(ResourceAllocateTask.java:27)
at com.pmease.quickbuild.resource.ResourceAllocateTask.reduce(ResourceAllocateTask.java:13)
at com.pmease.quickbuild.grid.GridTaskFuture.get(GridTaskFuture.java:102)
at com.pmease.quickbuild.grid.GridTaskFuture.get(GridTaskFuture.java:106)
at com.pmease.quickbuild.stepsupport.StepExecutionTask.map(StepExecutionTask.java:86)
at com.pmease.quickbuild.stepsupport.StepExecutionTask.map(StepExecutionTask.java:19)
at com.pmease.quickbuild.grid.GridImpl.execute(GridImpl.java:83)
at com.pmease.quickbuild.stepsupport.StepProcessJob.executeStepAwareJob(StepProcessJob.java:38)
... 8 more
Caused by: java.lang.IllegalArgumentException: The validated object is null
at org.apache.commons.lang.Validate.notNull(Validate.java:222)
at com.pmease.quickbuild.DefaultBuildEngine.allocateResource(DefaultBuildEngine.java:2278)
at com.pmease.quickbuild.resource.ResourceAllocateJob.execute(ResourceAllocateJob.java:36)
at com.pmease.quickbuild.grid.GridJob.run(GridJob.java:106)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

Thanks for the help!