I'm working within a sheet and trying to calculate the number of days between two dates. 
    
        
             
    
Above is a picture of what I'm seeing and my syntax is below. 
=NETWORKDAYS([Start Date]@row, [Date Completed]@row)
I've tried to add IFERROR in a couple places and it didn't help with anything unfortunately. My Task Duration is set as a Number/Text. I've also tried setting it to 'Date' to see if that made any difference, but no luck unfortunately. 
Any guidance or direction could be greatly appreciated. 
Thanks!