ORA-12519, TNS:no appropriate service handler found

Hi All, 

I have installed Oracle 11g R2 licensed version in linux operation system (RED Hat Linux Version 5.5) But i am getting below mentioned error. I figured that it might be due to the  limited concurrent connections. so i increased the concurrent connection to 300. But still i am getting the below errors. Please advise. 

alter system set processes=300 scope=spfile;

Caused by: java.sql.SQLException: Listener refused the connection with the following error:

ORA-12519, TNS:no appropriate service handler found

The Connection descriptor used by the client was:

Thanks

Ravindranath Seetharamagowdu