New email notification on email icon

[viator]

Hi all;

I am using Samsung Tab with preinstalled 3.2 Honeycomb. Since a week a go, my tab behave abnormally where on the Email icon, showing numeric figure of unread email, but when I go deep to the application and have read all new incoming mail, figure unread email still showed (but in email icon and social hub icon).

So far I have:
- sort the list based on uread email: but could not find unread email
- delete all email on my inbox for the last 1 month: but no effect

Could somebody please telling me, how to get rid of this unread email figure?

Thanks, Viator