Thank you for your response. I was aware of the limit of units issue. That wasn't the case when that happened. I hadn't even built a single mobile unit when I suddenly couldn't build one. Also the message you've mentioned didn't show up. (In the last mission my buildings are getting attacked by missiles early, so I concentrated on building mining facilities, to have enough spice for repairs of buildings, and rocket turrets. Of course I also built factories for units, but, to save spice, no units.) P.S.: Maybe I had built too much rocket turrets. Does that affect how much mobile units I can build also? If yes, please correct that, in my opinion rocket turrets are buildings, not units.