2002 Toyota 4Runner will not keep running

At first they said it was a crank shaft sensor, when that was replaced and it still did not fix the problem, they said that the reluctor wheel around the timing unit was bad. They are telling me that this is all due to a bolt that was not properly tightened when the timing belt was changed. I had it changed 14 months ago, but it has only gone 20,000 miles or so. The place that changed it said that it was not possible for a bolt not tightened to specs to cause this, nor would it be possible to go 14 months with a bolt not tightened. Is it?