[Alneyan]

I have failed to obsolete AI designed ships in Adamant 014 twice when I took over. The ships did not use any kind of special technology, and I can build them just fine. The ships had also never been built, or had been destroyed in the first few turns.

So I either ran into a bug of the game, or I cannot remember what I am doing, and clicked twice on "Make Obsolete", or something along these lines.