Calculations days hours minutes (dd mm:hh)

Hello,
I used office 2003. In excell 2003 i used to format cells to dd hh:mm from dd/mm/yy hh:mm, in order to do calculations and i didn;t have a problem.
Now i m trying to do calculations with this format (dd hh:mm) in excell 2007 and it shows value error in the cell where it is the result.

thank you in advance