Why does a valid Texture not reach the Shader? (Direct3D9)

Hello everyone I'm currently trying to create a deferred renderer for my graphics engine using c# and SlimDX. As a resource I use this tutorial which is very helpful eventhough it's intended for XNA. But right now I'm stuck... I have my renderer set up to draw all geometry's color, normals and depth to seperate render target textures. This works. I can draw the resulting textures to the restored backbuffer as sprites and I can see that they contain just what they are supposed to. But when I try to pass those Textures to another shader, in this case to create a light map, weirds things happen. Here's how I draw one frame:

public bool RenderFrame(FrameInfo fInfo){
    if(!BeginRender()) //checks Device, resizes buffers, calls BeginScene(), etc.
         return false;
    foreach(RenderQueue queue in fInfo.GetRenderQueues()){
        RenderQueue(queue);
    }
    EndRender(); //currently only calls EndScene, used to do more
    ResolveGBuffer();
    DrawDirectionalLight(
        new Vector3(1f, -1f, 0), 
        new Color4(1f,1f,1f,1f), 
        fi.CameraPosition, 
        SlimMath.Matrix.Invert(fi.ViewProjectionMatrix));
}

private void ResolveGBuffer() {
    if(DeviceContext9 == null || DeviceContext9.Device == null)
        return;
    DeviceContext9.Device.SetRenderTarget(0, _backbuffer);
    DeviceContext9.Device.SetRenderTarget(1, null);
    DeviceContext9.Device.SetRenderTarget(2, null);
}

private void DrawDirectionalLight(Vector3 lightDirection, Color4 color, SlimMath.Vector3 cameraPosition, SlimMath.Matrix invertedViewProjection) {
    if(DeviceContext9 == null || DeviceContext9.Device == null)
        return;
        DeviceContext9.Device.BeginScene();
       _directionalLightShader.Shader.SetTexture(
           _directionalLightShader.Parameters["ColorMap"], 
           _colorTexture);
       _directionalLightShader.Shader.SetTexture(
           _directionalLightShader.Parameters["NormalMap"], 
           _normalTexture);
       _directionalLightShader.Shader.SetTexture(
           _directionalLightShader.Parameters["DepthMap"], 
           _depthTexture);
       _directionalLightShader.Shader.SetValue<Vector3>(
           _directionalLightShader.Parameters["lightDirection"], 
           lightDirection);
       _directionalLightShader.Shader.SetValue<Color4>(
           _directionalLightShader.Parameters["Color"], 
           color);
       _directionalLightShader.Shader.SetValue<SlimMath.Vector3>(
           _directionalLightShader.Parameters["cameraPosition"], 
           cameraPosition);
       _directionalLightShader.Shader.SetValue<SlimMath.Matrix>(
           _directionalLightShader.Parameters["InvertViewProjection"], 
           invertedViewProjection);
       _directionalLightShader.Shader.SetValue<Vector2>(
           _directionalLightShader.Parameters["halfPixel"], 
           _halfPixel);

       _directionalLightShader.Shader.Technique = 
           _directionalLightShader.Technique("Technique0");

       _directionalLightShader.Shader.Begin();
       _directionalLightShader.Shader.BeginPass(0);
       RenderQuad(SlimMath.Vector2.One * -1, SlimMath.Vector2.One);
       _directionalLightShader.Shader.EndPass();
       _directionalLightShader.Shader.End();
       DeviceContext9.Device.EndScene();
}

Now when I replace the call to DrawDirectionalLight with some code to draw _colorTexture, _normalTexture and _depthTexture to the screen everything looks ok, but when I use the DrawDirectionalLight function instead I see wild flickering. From the output of PIX it looks like my textures do not get passed to the shader correctly:

Following the tutorial the texture parameters and samplers are defined as follows:

float3 lightDirection;
float3 Color;
float3 cameraPosition;
float4x4 InvertViewProjection;
texture ColorMap;
texture NormalMap;
texture DepthMap;

sampler colorSampler = sampler_state{
Texture  = ColorMap;
AddressU = CLAMP;
AddressV = CLAMP;
MagFilter= LINEAR;
MinFilter= LINEAR;
MipFilter= LINEAR;
};

sampler depthSampler = sampler_state{
Texture  = DepthMap;
AddressU = CLAMP;
AddressV = CLAMP;
MagFilter= POINT;
MinFilter= POINT;
MipFilter= POINT;
};

sampler normalSampler = sampler_state{
Texture  = NormalMap;
AddressU = CLAMP;
AddressV = CLAMP;
MagFilter= POINT;
MinFilter= POINT;
MipFilter= POINT;
};

Now my big question is WHY? There are no error messages printed to debug output.

EDIT:

the rendertargets/textures are created like this:

_colorTexture = new Texture(DeviceContext9.Device,
            DeviceContext9.PresentParameters.BackBufferWidth,
            DeviceContext9.PresentParameters.BackBufferHeight,
            1,
            Usage.RenderTarget,
            Format.A8R8G8B8,
            Pool.Default);

        _colorSurface = _colorTexture.GetSurfaceLevel(0);

        _normalTexture = new Texture(DeviceContext9.Device,
            DeviceContext9.PresentParameters.BackBufferWidth,
            DeviceContext9.PresentParameters.BackBufferHeight,
            1,
            Usage.RenderTarget,
            Format.A8R8G8B8,
            Pool.Default);

        _normalSurface = _normalTexture.GetSurfaceLevel(0);

        _depthTexture = new Texture(DeviceContext9.Device,
            DeviceContext9.PresentPar开发者_运维知识库ameters.BackBufferWidth,
            DeviceContext9.PresentParameters.BackBufferHeight,
            1,
            Usage.RenderTarget,
            Format.A8R8G8B8,
            Pool.Default);

        _depthSurface = _depthTexture.GetSurfaceLevel(0);

EDIT 2:

The problems seems to lie in the directionalLightShader itselft since passing other regular textures doesn't work either.

The answer to my problem is as simple as the problem was stupid. The strange behaviour was caused by 2 different errors:

1. I was just looking at the wrong events in PIX. The textures we passed correctly to the shader but I didn't see it because it was 'hidden' in the BeginPass-event (behind the '+').
2. The pixel shader which I was trying to execute never got called because vertices of the fullscreen quad I used to render were drawn in clockwise order... my CullMode was also set to clockwise...

Thanks to everyone who read this question!