You are not doing anything wrong, it's just that we don't support solo mining yet. There is noting really hard to prevent us from implementing it but in 99% of the cases it's not very practical with the difficulty of most coins. However if there is enough interest (or at least after we implement more urgent features like control over clocks and voltages, and dual mining), we are going to implement it.

     Yes, you were spot on.   It was mainly wishful thinking on our part to assume that it would take more time before ASICs made siacoin GPU mining obsolete. Still we are too far into implementing dual mining with decred, so we are going to release it anyway whenever it is ready. Even if it is completely useless by then, at least we will have some experience with implementing it that would hopefully translate to some other coin that can be dual-mined with ethash profitably.