Thanks.
I tried doing this but I'm still getting the error. Any comments is appreciated.
=SI([Completed Date]="","",SI(AND((JOURSEM([Date de fin],2))<(JOURSEM([Créé],2)),((JOURSEM([Créé],2))-(JOURSEM([Date de fin],2)))>1),(((DATEDIF([Créé],[Date de fin],"D")+1))-(PLANCHER(DATEDIF([Créé],[Date de fin],"D")+1)/7,1)*2)-2),(((DATEDIF([Créé],[Date
de fin],"D")+1))-(PLANCHER((DATEDIF([Créé],[Date de fin],"D")+1)/7,1)*2))))