Oracle Error ORA-00018 maximum number of sessions exceeded

Cause: In Oracle pl sql all session state objects are in use.

Action: You ust increase the value of the SESSIONS initialization o kill one session.

Edit init< sid >.ora. If there is NO entry for SESSIONS , create one. do a clean shutdown of database. startup the database with this init< sid >.ora. Check whether the change is affected. if so, create the spfile from this pfile because spfile is default in 9i. do a clean shutdown. startup normal and then look for the session parameter. processes=150 you can change that value of parameter processes and save it in your init.ora

So you must:

Increase the value of the SESSIONS initialization parameter in thet init< sid >.ora and If there is NO entry for SESSIONS , create it. Then stop service of databse.

Startup the database with this init< sid >.ora.
Check whether the change is affected.
if so, create the spfile from this pfile ( because spfile is default in 9i).
do a clean shutdown.
startup normal.