"I just think that purely mathematical errors are relatively rare"
It's more common than you would think.
Math error equals loss of Mars orbiter
NASA reported Sept. 30 that it had lost the $125 million Mars Climate Orbiter because the force exerted by the orbiter's thrusters remained in the system of units based on pounds and feet rather than being converted to metric.
http://findarticles.com/p/articles/mi_m1200/is_15_156/ai_571...