Exception while undeploying application in WebSphere Liberty Profile

I am trying to test my JEE application with Arquillian running under WebSphere Liberty Profile 8.5.5.4. My Arquillian tests run against an EJB and a REST service.

All the tests run successfully. However, the JUnit test process always ends with an exception:

org.jboss.arquillian.container.spi.client.container.DeploymentException: Exception while undeploying application.

at org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer.undeploy(WLPManagedContainer.java:419)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController$4.call(ContainerDeployController.java:205)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController$4.call(ContainerDeployController.java:185)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController.executeOperation(ContainerDeployController.java:271)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController.undeploy(ContainerDeployController.java:184)

...

Caused by: org.jboss.arquillian.container.spi.client.container.DeploymentException: Unable to delete archive from apps directory

at org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer.undeploy(WLPManagedContainer.java:405)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController$4.call(ContainerDeployController.java:205)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController$4.call(ContainerDeployController.java:185)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController.executeOperation(ContainerDeployController.java:271)

at org.jboss.arquillian.container.impl.client.container.ContainerDeployController.undeploy(ContainerDeployController.java:184)

I ran this with a trace that Gerhard suggested, and here is the relevant section of the trace:

Jun 24, 2015 11:14:18 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer undeploy
FINER: ENTRY
Jun 24, 2015 11:14:18 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer getServerXML
FINER: server.xml: /IBM/WLP8554/usr/servers/taskcalendar/server.xml
Jun 24, 2015 11:14:18 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer getServerXML
FINER: server.xml: /IBM/WLP8554/usr/servers/taskcalendar/server.xml
Jun 24, 2015 11:14:18 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer waitForMBeanTargetState
FINER: ENTRY
[AUDIT ] CWWKG0016I: Starting server configuration update.
[AUDIT ] CWWKG0028A: Processing included configuration resource: C:\IBM\WLP8554\usr\servers\taskcalendar\serverApplication.xml
[AUDIT ] CWWKG0028A: Processing included configuration resource: C:\IBM\WLP8554\usr\servers\taskcalendar\serverKeyStore.xml
[AUDIT ] CWWKG0028A: Processing included configuration resource: C:\IBM\WLP8554\usr\servers\taskcalendar\serverBasicUserRegistry.xml
[AUDIT ] CWWKG0028A: Processing included configuration resource: C:\IBM\WLP8554\usr\servers\taskcalendar\serverTesting.xml
[AUDIT ] CWWKG0017I: The server configuration was successfully updated in 0.043 seconds.
[AUDIT ] CWWKT0017I: Web application removed (default_host): http://dlwester:30080/task-calendar-ejb-task-calendar-bean-test/
[INFO ] SRVE0253I: [task-calendar-ejb-task-calendar-bean-test] [/task-calendar-ejb-task-calendar-bean-test] [ArquillianServletRunner]: Destroy successful.
[INFO ] OpenWebBeans Container was stopped for context path, [/task-calendar-ejb-task-calendar-bean-test]
[INFO ] CNTR4003I: The task-calendar-ejb-task-calendar-bean-test.war EJB module in the task-calendar-ejb-task-calendar-bean-test application is stopping.
[INFO ] CNTR4004I: The task-calendar-ejb-task-calendar-bean-test.war EJB module in the task-calendar-ejb-task-calendar-bean-test application has stopped successfully.
[AUDIT ] CWWKZ0009I: The application task-calendar-ejb-task-calendar-bean-test has stopped successfully.
Jun 24, 2015 11:14:18 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer waitForMBeanTargetState
FINER: RETURN
Jun 24, 2015 11:14:18 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer getAppDirectory
FINER: appDir: /IBM/WLP8554/usr/servers/taskcalendar/apps
Jun 24, 2015 11:14:19 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer stop
FINER: ENTRY
Jun 24, 2015 11:14:19 AM org.jboss.arquillian.container.was.wlp_managed_8_5.WLPManagedContainer stop
FINER: RETURN