Story about future where everyone's brain is uploaded into a computer which is running a world simulation. The outside real Earth is dead, and the computers have been set up with all intents of "running forever" (note, death of our Sun will happen before heat death of the universe, but whatever). Systems are redundant, and made as bullet proof as ever possible. Some power source is used that would be uninterruptible (worldwide solar grid, geothermal, etc). To make this "life" livable all the people in the networked world agreed to forget that they once lived "outside" and that they are running in a simulation of the world inside a computer. Maybe one or two had to keep that knowledge, it's your story, whatever. This is our colony ship to help humanity survive. But now, some 50 or hundred years later the systems begin to fail, which has noticeable effects into the virtual world (program resets, people just disappearing, glitches in the "resolution" of the world). So the people inside the simulation need to both figure out that they are in a simulation and then how to fix their world. Are there external robots meant to maintain the physical computers they all exist in? Is there a way they can manifest outside And what does that do to their society to realize that they are running in a simulation? Remember, they all choose to forget so they could live "happily" inside a computer simulation.