Problem: We're in the situation where the spreadsheet in which we use NumXL for seasonal adjustment isn't calculating. The file is set to manual calculation, so I hit F9 to trigger re-calculation, they all returns #N/A's.
The spreadsheet file contains tens-to-hundreds of time-series models, and they worked perfectly before, but suddenly this issue pops up.
Furthermore, If I copy any of the time series data-set and its models to a new workbook file, the models work fine in that file.
Save the workbook file to a new file (File -> Save As), close the workbook, and open the new workbook file. This should take care of the problem.