I keep getting an access violation error while im trying to fill my terrain index buffer. This problem has come out in many versions of my terrain engine and i fiddle with the code and it goes away but i havnt really changed anything. So now im trying to figure out exactly what im doing wrong so i can stop it happening in future projects. here is the structure of my terrain patch

	struct sTerrainPatch
	{
		LPDIRECT3DTEXTURE8 PatchTexture;
		LPDIRECT3DVERTEXBUFFER8 PatchVB;
		LPDIRECT3DINDEXBUFFER8 PatchIB;
		int NumVertices;
		int NumIndices;
		unsigned short *ind;
		int x,y;	//Position the the patch within the heightmap

		bool inited;
		bool filled;
	};

and here is the source of the fill index buffer procedure

cTerrainEngine::FillPatchIndexBuffer(sTerrainPatch *patch)
{
	HRESULT hr;
	int i,j;
	int currvert;

	hr = patch->PatchIB->Lock(	0,
								0,
								(BYTE**)&patch->ind,
								0);
	if(FAILED(hr))
	{
		//write the error to the error log and then try and

		//nicely quit the program

	}

	for(i=0;i<PATCHSIZE;i++)
		for(j=0;j<PATCHSIZE;j++)
		{
			currvert = (j*PATCHSIZEVERTS)+i;
			
			//Add the first tri of the tile

			patch->ind[patch->NumIndices++] = currvert;
			patch->ind[patch->NumIndices++] = currvert+1;
			patch->ind[patch->NumIndices++] = currvert+PATCHSIZEVERTS+1;

			//Add the second tri of the tile

			patch->ind[patch->NumIndices++] = currvert;
			patch->ind[patch->NumIndices++] = currvert+PATCHSIZEVERTS+1;
			patch->ind[patch->NumIndices++] = currvert+PATCHSIZEVERTS;
		}
		patch->PatchIB->Unlock();
}

if you need anything else i''ll post it up asap

Here the index buffer creation code

	device->CreateIndexBuffer((PATCHSIZE*PATCHSIZE)*6,								D3DUSAGE_WRITEONLY,								D3DFMT_INDEX16,								D3DPOOL_DEFAULT,								&patch->PatchIB);

What happens if you change

(PATCHSIZE*PATCHSIZE)*6, 

to

(PATCHSIZE*PATCHSIZE)*6*sizeof(unsigned short) 

The former sets the buffer''s size to PATCHSIZE*PATCHSIZE*6 bytes and the latter sets the size to the same number of shorts.