"Oh, no. We have the nanobots. They're everywhere, even the air. We're breathing them in and out right now. They're settling on our skin, crawling up from the ground. We're infested with them. That's the problem. What we don't have are the additional inoculations to protect us from them.

"Which means that the nanobots see us as foreign objects and are breaking us down. Reducing our clothing, our tools, our bodies into component molecules. We're being eaten, Padme.

"That's why the TARDIS wouldn't open. The key is so sensitive that even the smallest variation means it no longer fits. The nanobots may have only broken down the tinest portion of it so far, but it's enough that it's not the right key anymore."