Can`t play necrons after imperials

Just finished imperial campaign with the cutscene and was sent back to the main menu; tried to start the necron campaign (clicking "new campaign"), but didnt succeed, as it quotes: "you first have to do the prologue and the tutorial missions of the imperial campaign". Seems to be a bug. Tried to do the last mission several times and also tried to "steam repair" the game, still I cant launch the necron campaign. To quote a big (?) man in America: so sad...

Found the error: during the prologue mission, one of the tasks probably failed (i.e. shooting boarding torps at an already destroyed ship), thus I guess the prologue remained "unfinished" in the game code. By playing everything one again I finally managed to get access to the Necrons, although I have to say I am quite underwhelmed so far. But we`ll see...