Could not load Microsoft.DirectX.DirectSound

I try to build audio synth app from the example http://code.msdn.microsoft.com/wpf3osc

I get an error while running the application: Could not load file or assembly 'Microsoft.DirectX.DirectSound.dll' or one of its dependencies.  is not a valid Win32 application. (Exception from HRESULT: 0x800700C1)

There are Microsoft.DirectX and Microsoft.DirectX.DirectSound in the project references. (form C:\Windows\Microsoft.NET\DirectX for Managed Code\1.0.2902.0\)

I've just started with DirectX DirectSound. I don't understand why it could not be loaded... Please help me!

Microsoft Visual C# 2010 Express
DirectX SDK (June 2010)