Clipping plane issue

Im using a clip plane to render water reflection,refraction. Resources say to transform the plane to viewspace using this matrix(taken from riemers) Matrix worldViewProjection = currentViewMatrix * projectionMatrix; Matrix inverseWorldViewProjection = Matrix.Invert(worldViewProjection); inverseWorldViewProjection = Matrix.Transpose(inverseWorldViewProjection); However, this does not work at all, when i use the ordinary viewproj matrix, it seems to work. Why is this?