Fail to clean before build

Hi,

I have a branch that was building fine for couple month and now I start to get below error with each build. The folder is not held by another process according to Porcess Explorer. What could cause below problem?

java.lang.RuntimeException: com.atlassian.bamboo.repository.RepositoryException: Unable to clean source directory 'Z:\build\TRADE-MAF4-JOB1' Z:\build\TRADE-MAF4-JOB1\.git
at com.atlassian.bamboo.executor.RetryingTaskExecutor.rerun(RetryingTaskExecutor.java:144)
at com.atlassian.bamboo.executor.RetryingTaskExecutor.runTask(RetryingTaskExecutor.java:88)
at com.atlassian.bamboo.executor.RetryingTaskExecutor.retry(RetryingTaskExecutor.java:203)
at com.atlassian.bamboo.executor.RetryingTaskExecutor.retry(RetryingTaskExecutor.java:188)
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask.preRetrieveSourceCode(VcsCheckoutTask.java:217)
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask.execute(VcsCheckoutTask.java:124)
at com.atlassian.bamboo.task.TaskExecutorImpl.lambda$executeTasks$68(TaskExecutorImpl.java:273)
at com.atlassian.bamboo.task.TaskExecutorImpl$$Lambda$20/792998599.call(Unknown Source)
at com.atlassian.bamboo.task.TaskExecutorImpl.executeTaskWithPrePostActions(TaskExecutorImpl.java:202)
at com.atlassian.bamboo.task.TaskExecutorImpl.executeTasks(TaskExecutorImpl.java:273)
at com.atlassian.bamboo.task.TaskExecutorImpl.executePreparationTasks(TaskExecutorImpl.java:83)
at com.atlassian.bamboo.build.pipeline.tasks.PrepareBuildTask.call(PrepareBuildTask.java:74)
at com.atlassian.bamboo.v2.build.agent.DefaultBuildAgent.build(DefaultBuildAgent.java:196)
at com.atlassian.bamboo.v2.build.agent.BuildAgentControllerImpl$1.call(BuildAgentControllerImpl.java:132)
at com.atlassian.bamboo.v2.build.agent.BuildAgentControllerImpl$1.call(BuildAgentControllerImpl.java:123)
at com.atlassian.bamboo.variable.CustomVariableContextImpl.withVariableSubstitutor(CustomVariableContextImpl.java:215)
at com.atlassian.bamboo.v2.build.agent.BuildAgentControllerImpl.waitAndPerformBuild(BuildAgentControllerImpl.java:122)
at com.atlassian.bamboo.v2.build.agent.DefaultBuildAgent$1.run(DefaultBuildAgent.java:118)
at com.atlassian.bamboo.utils.BambooRunnables$1.run(BambooRunnables.java:49)
at com.atlassian.bamboo.security.ImpersonationHelper.runWith(ImpersonationHelper.java:31)
at com.atlassian.bamboo.security.ImpersonationHelper.runWithSystemAuthority(ImpersonationHelper.java:20)
at com.atlassian.bamboo.security.ImpersonationHelper$1.run(ImpersonationHelper.java:52)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.atlassian.bamboo.repository.RepositoryException: Unable to clean source directory 'Z:\build\TRADE-MAF4-JOB1' Z:\build\TRADE-MAF4-JOB1\.git
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask.cleanWorkingDirIfNeeded(VcsCheckoutTask.java:371)
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask.access$100(VcsCheckoutTask.java:57)
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask$2.call(VcsCheckoutTask.java:222)
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask$2.call(VcsCheckoutTask.java:218)
at com.atlassian.bamboo.executor.RetryingTaskExecutor.rerun(RetryingTaskExecutor.java:108)
... 22 more
Caused by: java.nio.file.DirectoryNotEmptyException: Z:\build\TRADE-MAF4-JOB1\.git
at sun.nio.fs.WindowsFileSystemProvider.implDelete(WindowsFileSystemProvider.java:266)
at sun.nio.fs.AbstractFileSystemProvider.delete(AbstractFileSystemProvider.java:103)
at java.nio.file.Files.delete(Files.java:1126)
at com.atlassian.bamboo.utils.BambooPathUtils.deleteNoThrow(BambooPathUtils.java:158)
at com.atlassian.bamboo.utils.BambooPathUtils.access$000(BambooPathUtils.java:28)
at com.atlassian.bamboo.utils.BambooPathUtils$1.postVisitDirectory(BambooPathUtils.java:97)
at com.atlassian.bamboo.utils.BambooPathUtils$1.postVisitDirectory(BambooPathUtils.java:74)
at java.nio.file.Files.walkFileTree(Files.java:2688)
at java.nio.file.Files.walkFileTree(Files.java:2742)
at com.atlassian.bamboo.utils.BambooPathUtils.cleanDirectory(BambooPathUtils.java:103)
at com.atlassian.bamboo.util.BambooFileUtils.cleanDirectory(BambooFileUtils.java:770)
at com.atlassian.bamboo.plugins.vcs.task.VcsCheckoutTask.cleanWorkingDirIfNeeded(VcsCheckoutTask.java:365)