Delphi中的CreateVertexDeclaration错误

我有简单的声明：

uses ...
  Winapi.Direct3D9, Winapi.DXTypes, Winapi.D3DX9,

var
  g_pVertexDeclaration: IDirect3DVertexDeclaration9 = nil;
const
  decl: array [0 .. 4] of TD3DVertexElement9 = (
    (Stream: 0; Offset: 0; _Type: D3DDECLTYPE_FLOAT3; Method: D3DDECLMETHOD_DEFAULT;
    Usage: D3DDECLUSAGE_POSITION; UsageIndex: 0),
    (Stream: 0; Offset: 3 * sizeof(single); _Type: D3DDECLTYPE_FLOAT3; Method: D3DDECLMETHOD_DEFAULT;
    Usage: D3DDECLUSAGE_NORMAL; UsageIndex: 0),
    (Stream: 0; Offset: 6 * sizeof(single); _Type: D3DDECLTYPE_FLOAT2; Method: D3DDECLMETHOD_DEFAULT;
    Usage: D3DDECLUSAGE_TEXCOORD; UsageIndex: 0),
    (Stream: 0; Offset: 8 * sizeof(single); _Type: D3DDECLTYPE_FLOAT2; Method: D3DDECLMETHOD_DEFAULT;
    Usage: D3DDECLUSAGE_TEXCOORD; UsageIndex: 0),
    (Stream: $FF; Offset: 0; _Type: D3DDECLTYPE_UNUSED; Method: TD3DDeclMethod(0);
    Usage: TD3DDeclUsage(0); UsageIndex: 0) //({D3DDECL_END})
    );

记录错误的功能

function CheckDxError(e: dword): boolean;
begin
  if Failed(e) then begin
    raise Exception.Create(format('dx error %d: %s, %s', [(e shr 16) and $7FFF, DXGetErrorString9(e),
      DXGetErrorDescription9(e)]));
    exit(false);
  end;
  result := true;
end;

我dx error 0: E_FAIL, An Undetermined error occured在

  CheckDxError(m_pd3dDevice.CreateVertexDeclaration(@decl, g_pVertexDeclaration));

DirectX 9，设备等在调用之前进行了初始化（并且代码没有着色器，我试图研究着色器），使用只有第一个位置和D3DDECL_END的decl数组，此代码中没有错误。但是我的顶点着色器包含4个输入值，并且使用DirectX SDK中的fxc.exe进行编译时没有错误。

struct VSInput
{
    float3 Pos : POSITION;
    float3 Normal : NORMAL;
    float2 TexcoordUV : TEXCOORD0;
    float2 TexcoordST : TEXCOORD1;
};

为什么会发生此错误，以及如何避免？