SUM not working on values calculated using formulas

I can't share a preview of the document due to the nature of it. 

Data in our accident sheet. 

Columns T & U are the sickness dates. The cell is in date format.

Column V is =NETWORKDAYS (T00, U00). The cell is in general format

I wanted to add the values in V38:V250 and put it in cell F6. 

In cell F6 I typed in general cell format. =SUM(V38:V250) and instead of X day of numbers it is showing -62006. When it should read 62. I tried removing the formula from the V cells and just manually typing the number in and it still doesn't read the correct figure.