"ORA-02391: exceeded simultaneous SESSIONS_PER_USER limit" when trying to run a query. (4226282)

I am in the Query Builder (QB) and I click and drag a table from the object palette to the QB. I select all columns, create a where clause, then click the Run icon at the bottom. I then get the error "ORA-02391: exceeded simultaneous SESSIONS_PER_USER limit".

The query will not run. I can click OK to this message and nothing else happens.

A single-session or limited session user account has been used to login to the database.

Same error will come up in general if any session limitation is exceeded (not just single-session limit).

RESOLUTION 1:
Adjust option setting for TDA to minimize number of connections it makes. Go to Tools menu | Options | Editor | General | un-check the "Use individual connection for each open editor" option | restart Toad | and then re-test the issue.

RESOLUTION 2:
Use another user account that can have more session opened at a time.

RESOLUTION 3:
Increase the SESSION_PER_USER value of current user's profile.

Verify if you have an Oracle profile set up for your user, and verify if that profile has set your user to a limited number of sessions (SESSIONS_PER_USER).

Depending on the number of sessions you're limited to and the number of session you have open for your user, you may error out when trying to run a query.

Toad for Data Analysis will run on multiple sessions, depending on what window you're working with and what you are trying to do. You may not have opened the sessions manually, but Toad will have opened sessions to carry out its work in the background.