Cubase 5.1 | Playback failed problem?

Always when i run cubase , i see this Error :

Enter the image:
http://imagizer.imageshack.us/a/img843/8720/nw59.png

What is the problem and how do i solve it please?
thanks!

Are you using a proper ASIO audio interface, or are you using a built in audio card in say, a laptop? Normally you select your suitable audio card as the ASIO device.