ORA-12520: TNS:listener could not find available handler for requested type of server

Version:

DB Version: 12.1.0.2.0

Issue: 

Connections to the DB are not happening either from sqlplus or from sqldeveloper. Tnsping command works fine

Error:

ORA-12520: TNS:listener could not find available handler for requested type of server. 

Reason:

When we log on to the DB host and connects directly without the tns service name, we get the actual error.

ORA-00020: maximum number of processes (300) exceeded

The error is due to Processes parameter value set in the database getting exceeded.

Fix:

Increase the parameter value in the database. We need to restart the DB to make the change effective since it is not dynamically modifiable.

SQL> alter system set processes=1000 scope=spfile;

System altered.

Shutdown and restart DB