ORA-12519: TNS:no appropriate service handler found error

ORA-12519: TNS: no appropriate service handler found error

The real problem lies in the PROCESSES parameter

All you need to do is the few simple steps as the following:-

1. Run SQL*Plus and login as SYSTEM. 
2. Run the command “alter system set processes=3000 scope=spfile;” 
3. VERY IMPORTANT is to Restart the database.