java - [BlackBerry - Java]Error: Module 'My_Project' must be signed with the RIM Runtime Code Signing Key (RTT)

Question

In the BlackBerry Java project, I try to add a feature to make sure the app can running on the backgroup.It runs normally on BB's emulator but failed with an error while run in the device.

Error: Module 'My_Project' must be signed with the RIM Runtime Code Signing Key (RTT)

the problem occurs in code as below:

    private ApplicationIndicatorRegistry reg;
    private ApplicationIndicator indicator;
    public static  ApplicationIndicator AppIndi;
    public AfmobiMobile() {
        testMobile = this;

        reg=ApplicationIndicatorRegistry.getInstance();
        EncodedImage img=EncodedImage.getEncodedImageResource("ic2.png");
        ApplicationIcon icon =new ApplicationIcon(img);
        indicator=reg.register(icon, false, true);
        AppIndi=reg.getApplicationIndicator();
}

All open handles to this volum would then be invaild.