Outlook 2010 not showing recently contact in the address bar

Dear All,
can someone help me solve this problem.
Normally, all the people I have sent mails to before appear in the adrress bar the moment I press a letter in the person’s name or email address. all of a sudden, this does not work anymore and even those in my organization does not appear when I press a letter from from their names. the only chance I have is to click “To” then I search through the global address list manually before I can have the receipient email address.

I really need help on this.