Enterprise Manager cannot connect to 11g database instance In Oracle 11g when we are opening OEM in browser it is showing the following message :

"Enterprise Manager is not able to connect the database instance."
Listener status is showing Up and 
Agent Connection to instance the status is showing unavailable.

please provide a solution.

I am attaching a screenshot of my problem. I still did not find any solution yet.plz help
You may need to resecure the agent. Here is a link that should help.

http://jhdba.wordpress.com/2008/12/10/clearing-an-enterprise-manager-agent-that-fails-to-upload/