First, what do you mean by "not working"? Do you get an error? An
incorrect result?

Is your add-in installed in XL, as well as on your HD (e.g.,
Tools/Add-ins...)

is r3 earlier than u3?

In article ,
"Al H." wrote:

I have been successfully using this function for quite some time. My formula
is (=if(t30,networkdays(r3,u3)," ") where t3 is a date also. Before you
ask, yes, I have the analysis tool pack add-in. The only difference is I
have switched over to the new XP operating system. Any ideas?