There is a stunning error in your code. It should read
Code:
// Creates a volume texture from the given filename
LPDIRECT3DVOLUMETEXTURE9 shd_voltex_create(STRING *filename)
{
	LPDIRECT3DVOLUMETEXTURE9 temptex;
	HRESULT res = D3DXCreateVolumeTextureFromFile((LPDIRECT3DDEVICE9)pd3ddev, filename, &temptex);
	if(res != S_OK)
	{
		printf("error: %x", res);
		return NULL;
	}
	return temptex;
}

What is _chr anyways?