How do I update my function syntax to stop getting the #INVALID DATA TYPE error?

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!