Well, it would be good to see also the actual values of your expressions / fields you are using in networkdays() function.
Or even better, could you post a small sample QVW that demonstrates your issue?
In general, check that FStatusDate precedes TransmDate:
Returns the number of working days (Monday-Friday) between and including start_date and end_date taking into account any optionally listed holidays. All parameters should be valid dates or timestamps.
And also double check that FStatusDate reference as well as TransmDate return a value to your expression, and only a single value:
=FStatusDate & ' - ' & TransmDate
Note also that one of your expressions uses TransmDate as expression label.