java.rmi.server.ExportException: object already exported

[rin perez]

hello, i'm having trouble with UnicastRemoteObject.exportObject(); and in using callbacks i always have this exception:
java.rmi.server.ExportException: object already exported

here's my code:

CallbackImplementation m;
try {
m = new CallbackImplementation(u);
UnicastRemoteObject.exportObject(m);
mess.logIn(m);
} catch (Exception e) {
e.printStackTrace();
}

[Nitesh Kant]

Are you doing an UnicastRemoteObject.unexport() before exporting again?