Occasional Visitor

I have 2 nearly identical spreadsheets each with a sheet that calculates income taxes on wages.  Part of the calculation is circular, so I have chosen the ENABLE ITERATIVE CALCULATIONS with 100 Iterations in the File Options area. In the 2018 version of this calculation, it works, no errors.  I updated the 2018 spreadsheet to include 2019 tax rates, very few other changes.  But in the 2019 version, the circular formulas all indicate #REF errors.  The formulas  are identical in the two files.  


How can I find the source of the errors?