Whenever I end my turn at 190, the usual progression happens, etc. Once all the other AI have taken their turn and 191 comes about, I get two events that pop up simultaneously. The first one is "The Doom Tide" announcing that the forces of Chaos have been beaten back, but are reforming and the only way to finally defeat them is killing Archaon the Everchosen. Before it can be read through though, and me click to acknowledge it, I get a pop up about the Warpstone Trade, either take control or leave it, I usually leave it, screw Chaos.
After I get through those though, I can't move my units, the cursor has an 'x' on it. I can recruit, build, apply skill points, but can't move my units, can't end my turn, and can't save the game.