I can't get through the Garden level

Hey everybody. I've taken care of everything I should need to do to get through the Garden level, except that I can't activate the Trunk Gate. I've got an engineer sitting next to it, there are no more virii on the map, all the buildings are under my control, etc. but I can't get the Trunk Gate to turn on. What's going on?

You have tried capturing the associated control tower, right? Not the gate itself.

Well, I went back and tried playing again and it turns out I had NOT taken control of the control building. I could have sworn I did, but sometimes it's hard to tell whether the lights are blinking red or yellow.

Anyway, I'm onto Containment and am getting stuck there on killing that spore generator. Good game, though.