ORA-00019

ORA-00019 : maximum number of session licenses exceeded Cause : All licenses are in use. Action : Increase the value of the LICENSE MAX SESSIONS 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 license max session initialization parameter from the sqlplus prompt

sql>alter system set license_max_sessions = (number of session i.e.50) scope = spfile;

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