How to get rid of "maximum user connections" error?

I am using MySQLi for my webapp but whenever I want to visit some particular page, I get mysqli_connect() [function.mysqli-connect]: (42000/1203): User ***_user already has more than 'max_user_connections' active connections. I tried already to close all connections but this does not improve the situation. Is there a way to know exactly what connections are open at any particular moment or any other useful data that can help me resolve this issue ? BTW, I'm using PHP 5.2.17 and MySQL 5.1.