GWT RPC XSRF protection - Invalid RPC token

i followed the instruction as per http://code.google.com/webtoolkit/doc/latest/DevGuideSecurityRpcXsrf.html
with gwt's eclipse sample. but, i got the

[ERROR] javax.servlet.ServletContext log: Exception while dispatching
incoming RPC call
com.google.gwt.user.server.rpc.UnexpectedException: Service method
'public abstract com.google.gwt.user.client.rpc.XsrfToken
com.google.gwt.user.client.rpc.XsrfTokenService.getNewXsrfToken()'
threw an unexpected exception:
com.google.gwt.user.client.rpc.RpcTokenException: Invalid RPC token
(Session cookie is not set or empty! Unable to generate XSRF cookie)
at
com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:
385)
...

what else is missing? or what wrong with this -

/**
* Send the name from the nameField to the server and wait for a
* response.
*/
private void sendNameToServer() {
// First, we validate the input.
errorLabel.setText("");
final String textToServer = nameField.getText();
if (!FieldVerifier.isValidName(textToServer)) {
errorLabel.setText("Please enter at least four characters");
return;
}

// Then, we send the input to the server.
sendButton.setEnabled(false);
textToServerLabel.setText(textToServer);
serverResponseLabel.setText("");

XsrfTokenServiceAsync xsrf = (XsrfTokenServiceAsync) GWT
.create(XsrfTokenService.class);
((ServiceDefTarget) xsrf).setServiceEntryPoint(GWT
.getModuleBaseURL() + "xsrf");
xsrf.getNewXsrfToken(new AsyncCallback<XsrfToken>() {

public void onSuccess(XsrfToken token) {

((HasRpcToken) greetingService).setRpcToken(token);

// make XSRF protected RPC call
greetingService.greetServer(textToServer,
new AsyncCallback<String>() {
public void onFailure(Throwable caught) {
// Show the RPC error message to the
// user
dialogBox
.setText("Remote Procedure Call - Failure");
serverResponseLabel
.addStyleName("serverResponseLabelError");
serverResponseLabel
.setHTML(SERVER_ERROR);
dialogBox.center();
closeButton.setFocus(true);
}

public void onSuccess(String result) {
dialogBox
.setText("Remote Procedure Call");
serverResponseLabel
.removeStyleName("serverResponseLabelError");
serverResponseLabel.setHTML(result);
dialogBox.center();
closeButton.setFocus(true);
}
});
}

public void onFailure(Throwable caught) {
try {
throw caught;
} catch (RpcTokenException e) {
// Can be thrown for several reasons:
// - duplicate session cookie, which may be a sign
// of a cookie
// overwrite attack
// - XSRF token cannot be generated because session
// cookie isn't
// present
} catch (Throwable e) {
// unexpected
}
}
});
}

--
You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group.
To post to this group, send email to google-web-toolkit@googlegroups.com.
To unsubscribe from this group, send email to google-web-toolkit+unsubscribe@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.