Using Networkdays function problem

[Bright]

Hi all,

When I use the networkdays and workday functions in Excel2003, the library
path is displayed in the front of the function name.

For example:
= 'C:\Program Files\Microsoft Office
Project\OFFICE11\LIBRARY\ANALYSIS\ATPVBACS.XLA'!NETWORKDAYS(D1,D2)

But it also work in this way without the library path in another machine.
= NETWORKDAYS(D1,D2)

How can I make it work without the library path?

Thanks in advance,