If there was a cog in your manufacturing machine that was well worn and slips and causes the rivets on your widget to be out of specs and tolerance levels, what would you do with the cog?
rbwhitaker: "but people aren't cogs...." This is the challenge, isn't it: treating people well, making them feel needed, wanted, valuable, while make the unpopular, non emotional decisions treating us human capability enablers exactly like tool enablers, system enablers, process enablers, money enablers...because that is exactly what we are. The hard, unpopular truth is companies, and their projects, do not exist so people have some place to go everyday. We are there to enable a capability, and we go away when we are no longer needed. We may not like how that sounds, but our feelings are not relevant.
The performance curve, if you believe it is normally distributed, says you will most likely have very average people on the job. Current thinking says the curve is not normally distributed at all, but instead skewed to the left, i.e., positively skewed. This means few produce the most; most produce little. These few individuals who "repeatedly" perform poorly are very unlikely they will even approach the MODE much less climb to be a high performer. They could, just not likely. It's a hard, crappy decision, but you're the PM. You HAVE to make the tough decisions. And you HAVE to consider what we know about human work behavior. And you have to deliver the goods. This means, act like a leader and replace the cog and turn the machine back on and deliver.