[Dany123]

I have problem in connecting to oracle database through netbeans IDE7 after I have typed in the host,SID,username,password. But i only receive a message which says "cannot establish a connection to jdbc:oracle:thin:@localhost:1521:EM using oracle.jdbc.OracleDriver (Listener refused the connection with the following error: ORA-12505, TNS:listener does not currently know of SID given in connect descriptor  )". I do not know the next thing to do. Please can some one help me?