Gmail mails not downloading in Outlook

Hello,
I had configured my gmail id on outlook express 2003 sometime back, and it was working fine till recently.
But now, when i try downloading the mails on outlook, it shows 'downloading 1 of 1' even when I can see several emails in my inbox on gmail. Sometimes it doesnt show any new message (nothing gets downloaded on outlook), when there are several new ones in gmail inbox. Please advice how to sort out this problem urgently.

Regards,
Ashley