[Koha] Member number is not auto-calculated

Hi every one, My name is Tarek Mehrem, Egyptian. I've been using Koha since 2003 and i find it a very good system. I have this problem: I'm using Koha 2.2.4, but whenever i add a new member i find the auto-caculated number is not working although it is on and i have to put any number. Does any one know the solution? Best regards Tarek Mehrem BUE Librarian