What is happen:
If Pre-Execution Action in step is "Delete specified files on current node" and Directory passed as "Directory" parameter does not exists build faild with:

ERROR - Step 'master>COMPILATION' is failed.
    Directory does not exist:C:\buildagent\workspace\root\MultiTester\CoreTools\vobs\MultiTester
        at org.apache.tools.ant.taskdefs.Delete.handle(Delete.java:624)
        at org.apache.tools.ant.taskdefs.Delete.execute(Delete.java:570)
        at com.pmease.quickbuild.util.FileUtils.deleteFiles(FileUtils.java:403)
        at com.pmease.quickbuild.setting.step.executeaction.DeleteFiles.execute(DeleteFiles.java:59)
        at com.pmease.quickbuild.setting.step.executeaction.DeleteFiles$$EnhancerByCGLIB$$8ba8b0ef.CGLIB$execute$0(<generated>)
        at com.pmease.quickbuild.setting.step.executeaction.DeleteFiles$$EnhancerByCGLIB$$8ba8b0ef$$FastClassByCGLIB$$35f2f8fa.invoke(<generated>)
        at net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:215)
        at com.pmease.quickbuild.DefaultScriptEngine$Interpolator.intercept(DefaultScriptEngine.java:273)
        at com.pmease.quickbuild.setting.step.executeaction.DeleteFiles$$EnhancerByCGLIB$$8ba8b0ef.execute(<generated>)
        at com.pmease.quickbuild.stepsupport.Step.execute(Step.java:401)
        at com.pmease.quickbuild.stepsupport.StepJob.execute(StepJob.java:42)
        at com.pmease.quickbuild.grid.GridJob.run(GridJob.java:122)
        at java.lang.Thread.run(Unknown Source)

Cause:
Workspaces of all agents was cleared and there is no directories inside workspace

How it should work in my opinion:
If directory does not exists QuickBuild put information about this in log, and skip deleting files