Could not load file or assembly X or one of its dependencies. is not a valid Win32 application. (HRESULT: 0x800700C1)

OS: Windows 8.1 64

I tried to play multiple sounds in VB.Net with DirectX, there are no errors in my code. The problem is whenever the event is fired I get this error

System.BadImageFormatException was unhandled Message: An unhandled exception of type 'System.BadImageFormatException' occurred in System.Windows.Forms.dll Additional information: Could not load file or assembly 'Microsoft.DirectX.AudioVideoPlayback.dll' or one of its dependencies. is not a valid Win32 application. (Exception from HRESULT: 0x800700C1)

Then I set Target CPU to x86 and I got this error

System.IO.FileLoadException was unhandled Message: An unhandled exception of type 'System.IO.FileLoadException' occurred in System.Windows.Forms.dll Additional information: Mixed mode assembly is built against version 'v1.1.4322' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.

So far I have tried uninstalling-reinstalling DirectX SDK, Installing everything that has to do with DirectX and different sound files (.wav). Also I had to browse to load the .dlls, I couldn't find them under Reference Manager>Assemblies but now I cant even load them through browse so I use Imports Microsoft.DirectX.AudioVideoPlayback It will let me Import the rest .dlls except(Reference Manager wont even open them):

Microsoft.DirectX.AudioVideoPlayback.dll
Microsoft.DirectX.dll
Microsoft.DirectX.DirectSound.dll

the ones that I need. Is there a way to clean re-install them?

Target Framework: .Net Framework 4.5

CODE:

Dim MySound1 As New Microsoft.DirectX.AudioVideoPlayback.Audio("D:\path\sound_file.mp3")

MySound1.Play()

Let me know if you need to know anything else.

UPDATE: I changed the Target Framework to .Net Framework 3.5 and it works fine but only if the CPU Target is set to x86! Why is that?

You are using the olden Managed DirectX wrappers. Targeted to run on .NET 1.1, a framework version that never supported 64-bit code. These wrappers have been deprecated a long time ago, the 2.0 version never made it out of beta.

Changing your EXE's Platform Target to x86 is required, there is no 64-bit version of Managed DirectX and the DLLs contain native 32-bit code written in Managed C++. Furthermore, if you target .NET 4.0 or higher then you have to use a .config file that says that it is okay to load such an ancient assembly that expects native code to run well on .NET 1.1. It should look like this:

<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
  </startup>
</configuration>

The useLegacyV2RuntimeActivationPolicy attribute suppresses the error message you got. Whether it can actually run on 4.0+ isn't that clear, nobody uses these wrappers anymore. The usual advice is to switch to SharpDX or SlimDX instead.