No FICA calculated

We paid an individual a sum of money the beginning of January via an interim and no FICA calculated. It threw all the earnings into In Excess.  I suspect that someone fat fingered a "4" into the tax method, but is there a way I can prove that? they overrode the federal and the state taxes to a certain percentage so they were also on the tax override screen. While I find it unlikely that they did this "4" thing....it's no where near any field they would be entering.... I can't come up with another explanation.

Any idea how FICA did not calculate?