An invocation of org.jboss.remoting.Client.send() will cause the execution of an InboundRequestTask on the server, where InboundRequestTask.run() looks for the related org.jboss.remoting3.remote.InboundClient to execute the request. An invocation of Client.close() will result in the related InboundClient being removed from its map. Since the InboundRequestTask is executed in a separate thread, it is possible for the removal of the InboundClient to occur before the InboundRequestTask accesses it. The result is a NullPointerException.