ORA-12519 Listener refused the connection

ORA-12519 error while connecting to the database, I asked other developers to disconnect from the db and then I tried to connect to the database, this time no error!!! So I guess this is due to insufficient sessions. 

Execute the following commands to increase the session, process and transactions.

connect sys as sysdba;




alter system set processes = 150 scope = spfile;

alter system set sessions = 300 scope = spfile;

alter system set transactions = 330 scope = spfile;



shutdown immediate;

startup;

select name, value

from v$parameter

where name in ('processes', 'sessions', 'transactions');

Above commands copied from this link More info