在线程上显示Busy Indicator并启动应用程序：线程错误（调用线程无法访问此对象）

I'm developing a WPF application and following MVVM approach. I have to show the busy indicator on my log-in screen when an user click on the 'Enter' Button. On 'Enter' button I am having an ICommand named 'EnterCommand' which then check the authentication and then loads the MainWindow.I'm developing a WPF application and following