ORA-00020

ORA-00020 : maximum number of processes (string) exceeded Cause : All process state objects are in use. Action : Increase the value of the PROCESSES initialization parameter

To increase the value of the sessions:

1. login to you oracle as sysdba:
sqlplus "/ as sysdba"

2. use the following command to alter processes initialization parameter from the sqlplus prompt

sql>alter system set processes = (number of session i.e.150) scope = spfile;

3. restart your database to take effect.
at the sqlplus prompt enter
sql> shutdown immediate;
sql> startup;