Printing from another app - networkdays won't calculate?

I am dumping data from another program into excel and doing some calculations and then printing. The problem is that the "Networkdays" function which is part of the data analysis add-in will not seem to work. If I have the spreadsheet save and close with the data in there, when I open the file in Excel manually it works fine, but if I send the print command from my other program it errors out and just prints "#NAME?" error anywhere that the "NetworkDays" function is called. My theory is that when I am calling the instance of Excel from the other app, it is not loading the add-in, and therefore it errors out. My question is based on this assumption. If I assume properly, does anyone know how I would call the add in to be loaded when calling the instance of Excel from the other app? Any help would be greatly appreciated.