In the first week, I started the role of Database Administrator, one of the application support personnel had an issue connecting to the oracle database via toad IDE.

Let me walk you through how I resolved this with just two easy steps.

The first thing I did was ask for his username and checked if he was active in any session

select sid, serial# from v$session where username='username';

I noticed the affected user was currently logged in some other sessions, I got the sid and serial# of the sessions and terminated them.

alter system kill session '971,55477';

And there we have it!