vertex shader must minimally write all four components of POSITION

Though the POSITION semantic must be written out by the vertex shader, it cannot be read in by the pixel shader in ps_2_0. So, the fix is to write out the position twice, but one of those is not labeled as POSITION, it is instead labeled as a TEXCOORD0. Then, the pixel shader does not use the POSITION semantic variable, but uses the TEXCOORD0 instead. To the compiler it effectively means that the POSITION input to the pixel shader can be ignored.

right code:

float4x4 ViewProjection;

struct VS_INPUT
{
float4 Position : POSITION0;
float3 Normal : NORMAL0;
float2 tcBase:TEXCOORD0;
};

struct VS_OUTPUT
{
float4 Position : POSITION0;
float3 Normal : TEXCOORD1;
float2 tcBase:TEXCOORD2;
};

}

VS_OUTPUT vs_main( VS_INPUT Input )
{
VS_OUTPUT Output;

Output.Position = mul( Input.Position, ViewProjection );
Output.Normal = Input.Normal;
Output.tcBase = Input.tcBase;
return( Output );
}

sampler AmbOcclusion;
sampler DiffuseEnvironment;

struct PS_OUTPUT
{
float4 Position : TEXCOORD0;
float3 Normal : TEXCOORD1;
float2 tcBase:TEXCOORD2;
};

float4 ps_main(PS_OUTPUT Input) : COLOR0
{
// Sample the filtered environment map
float4 ambient = texCUBE(DiffuseEnvironment, Input.Normal);

// Sample the ambient occlusion map
float ambientOcclusion = tex2D(AmbOcclusion, Input.tcBase).r;
return ambient * ambientOcclusion;
}