In the shadow map VS shader:
OUT.Z = mul(float4(IN.Pos, 1.0f), WorldView).z;
I think you need WorldViewProj here. But call it LightViewProj instead for proper naming convention for the second pass.
Also you need to pass two floats zw, not just z. Then in PS you need to divide z by w:
OUT.Depth = IN.z / IN.w;