In Module1 of an xls file, I added a function like:

Function DiffWeekDays(a,b)
DiffWeekDays = somecalculatedvalue
End Function

I use this function in some cells and it works perfect.

However after some days, I open the file again.
In the cells I used the function, I see now: #NAME?
The function hasn't been changed in the meanwhile.

Has anybody some idea what's causing this?

Many thanks in advance!

best regards,
Joris.