D3DXMatrixReflect

What is wrong with the following code?

Code:

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D3DXPLANE mirrorPlane(0.0f, 0.0f, 1.0f, 0.0f); // xy plane
D3DXMATRIX R;
D3DXMatrixReflect(&R, &mirrorPlane);

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When I run the program, it crashes constantly due to the D3DXMatrixReflect call. When I use the debugger, it gives the error:

Unhandled exception at 0x6366b9b6 (D3DX10d_43.dll) in dX.exe: 0xC0000005: Access violation reading location 0xffffffff.

At the top of the call stack, the yellow arrow is pointing to:

> D3DX10d_43.dll!intelsse2_D3DXMatrixReflect() + 0x22 bytes

The program crashes maybe half of the time I try to run it. What is wrong?