I had a problem in my ejb-jar.xml file that was causing my EJB deployment to fail (I forgot package names when defining my local/local-home/ejb-class values). This is, of course, expected to fail, but then I couldn't undeploy by removing my jar file or overwriting it. To try again I had to shut down and restart JBoss.
The following error appears on the console about once a second after removing or overwriting the jar file:
11:11:10,187 INFO [MainDeployer] Undeploy di file:/C:/web/jboss-20010207/jboss-
11:11:10,203 ERROR [MainDeployer] Undeployment failed: file:/C:/web/jboss-200102
org.jboss.deployment.DeploymentException: URL not deployed