ExecutorService thread pool shutdown exception

Question

Hello,
We are developing a desktop application (no applets etc) on the Netbeans plaform. I am trying to add a thread pool via the Java5 ExecutorService. I think we have a very standard implementation using static methods - we copied it from some basic examples in blogs. Please see the class below.
Everything seems OK until I try to run shutdown. During the application shutdown we catch an exception that says
access denied (java.lang.RuntimePermission modifyThread)The exception is raised when running the ExecutorService "shutdown()" method.
Please note that this is a desktop application, and we DO check the permission with the SecurityManager (see code) and we do seem to have the correct permission (no exception raised during check).
Firstly, this is the first time we've used ExecutorService, so maybe we just have just implemented it incorrectly. Secondly, all "googling" on the issue reveals very little. It only seems to happen to applets.
ANY SUGGESTIONS, ADVICE, GUIDANCE, HINTS would be MUCH appreciated.
public final class ThreadPool {
    private static ExecutorService threadPool = Executors.newFixedThreadPool(3);
    public static void execute(Runnable worker) {
        threadPool.submit(worker);
    public static void shutdown() {
        SecurityManager s = System.getSecurityManager ();
        if (s!=null) {
            try {
                s.checkPermission(new RuntimePermission("modifyThread"));
                // we apparently have permission, so proceed to shutdown ...
                threadPool.shutdown();  // EXCEPTION RAISED HERE !!!!!
                threadPool.awaitTermination(15L, TimeUnit.SECONDS);
                threadPool.shutdownNow(); // brutal mop up
            } catch (Exception e) {
                logger.warn("ThreadPool.shutdown(): ex=" + e.getMessage());
}

Answer 1

You don't explain the context in which this application is launched - applications can be restricted by security policies too.
shutdown requires two permissions: one from the installed SecurityManager if any, and the other directly from the AccessController. Your installed SecurityManager may be saying "yes" while the AccessController says "no". There is a change in Java 6 such that only the security manager is queried.