As Southerners would say about the Practitioner Hotline, "bless their hearts."  Did you ask them what the difference is between a math error and a calculation error?  Maybe the idea they are trying to express is that "math error" is a technical term that embraces many entries on a tax return that have nothing to do with arithmetic.  But if you are using software, an error in arithmetic is highly unlikely.  

Form 8959 is Additional Medicare Tax.  Did your clients file joint returns?  Were the W-2s coded properly for each spouse?  I'm not sure that makes a difference, just a shot in the dark.  

Form 8960 is Tax on Investment Income.  Did your clients have any unusual items, like capital gains or S-Corp dividends?