Problem with JNI and Tomcat

Hi all.
I developed a JNI DLL to use with a Java Web Application.
This DLL is used to communicate over a RS232 port, and it must notice
any event that occurs on the port to the java application.
I tested it before with a Standalone app to make sure all works, and
then moved it to the web application. The problem is that in the
standalone app it's all ok, whilst in the web app I'm only able to call
JNI functions from java, but I can't call java methods from the JNI
DLL...here is the code involved, if you have any idea on how to solve
this problem is very appreciated!!!

The sequence of operations is the following:

1) From it.ribes.serialDriver.SerialPort class i call the
nativeOpenPort JNI function
2) the nativeOpenPort functions looks for the "notifyEvent" Java method
in the object that called it, in order to notify events when they
occurs, and saves it in the "eventNotifyMethod" of the SERIALPORT
structure
3) When an event occurs, the thread used for reception calls the
"notifyEvent" function in the DLL, which calls the Java method searched
in the step 2

The CSerialEx Class istansiate a thread which "listens" to the serial
port waiting for events, and when an event occurs calls the
"notifyEvent" in the DLL.

Thanks for any help, I'm a bit desperate... :(

==========
   JAVA
==========

--- SerialPort.java ---

public class SerialPort extends CommPort {
    SerialPortEventNotifier notifier;

    ...

    private native boolean nativeOpenPort(String port);

    /* Called from JNI DLL */
    private void notifyEvent(int eventType) {
        notifier.notifyEvent(eventType);
    }
    /* *********** */

    boolean open(int timeout) {
        return nativeOpenPort(this.port);
    }

    ...

}

--- CommPortIdentifier.java ---

public class CommPortIdentifier {
    static List portList = new LinkedList();

    public static final int PORT_SERIAL = 1;

    private String portName;
    private int portType;

    static {
        System.loadLibrary("RS232Driver_DLL");
    }

    private static native boolean nativeTestSerial(int port);

    public CommPort open(String application, int timeout) throws
PortInUseException {
        SerialPort serialPort = new SerialPort(this.portName);
        if(!serialPort.open(timeout))
            throw new PortInUseException(portName);
        return serialPort;
    }

    ...

}

=============
   JNI DLL
=============

--- it_ribes_serialDriver_serialPort.cpp ---

....

typedef struct
{
    CSerialEx *com;
    char port[10];
    jobject javaEventManager;
    jmethodID eventNotifyMethod;
    LPSTR rxBuffer;
    int rxBufferDim;
    int inputIndex;
    int outputIndex;
    int dataAvailable;
    HANDLE readingMutex;
    int rxTimeout;
    DWORD eventMask;
} SERIALPORT, *LPSERIALPORT;

/* This method is used to open the serial port */
JNIEXPORT jboolean JNICALL
Java_it_ribes_serialDriver_SerialPort_nativeOpenPort (JNIEnv *env,
jobject jobj, jstring port)
{
    LPSERIALPORT SerialPort = (LPSERIALPORT)malloc(sizeof(SERIALPORT));

    if(VM == NULL)
        env->GetJavaVM(&VM);

    LPSTR comPort = (LPSTR)env->GetStringUTFChars(port, 0);

    _strupr(comPort);
    strncpy(SerialPort->port,comPort,10);
    SerialPort->com = new CSerialEx(); // This is the class used to
communicate over the serial port (Overlapped I/O used)

    SerialPort->com->Open(comPort,0,0,true);
    SerialPort->javaEventManager = env->NewGlobalRef(jobj);
    jclass cls = env->GetObjectClass(SerialPort->javaEventManager);
    SerialPort->eventNotifyMethod =
env->GetMethodID(cls,"notifyEvent","(I)V");

    env->ReleaseStringUTFChars(port, comPort);

    return TRUE;
}

/* This method is called from the CSerialEx class to notify an event */
void NotifyEvent(CSerial::EEvent event, LPSTR port)
{
    void *voidenv = NULL;
    JNIEnv *env;

    LPSERIALPORT SerialPort = SearchSerialPort(port);
    int javaEvent = MapEvent(event);

    VM->AttachCurrentThread(&voidenv,NULL);
    env = (JNIEnv *)voidenv;

    if(javaEvent != 0)
    {
        env->CallVoidMethod(SerialPort->javaEventManager,
SerialPort->eventNotifyMethod, javaEvent);
    }

    VM->DetachCurrentThread();
}

....