How to solve ORA-02391 exceeded simultaneous SESSIONS_PER_USER limit

The error definition:

//  *Cause: An attempt was made to exceed the maximum number of
//          concurrent sessions allowed by the SESSION_PER_USER clause
//          of the user profile.
//  *Action: End one or more concurrent sessions or ask the database
//           administrator to increase the SESSION_PER_USER limit of
//           the user profile.

You need to adjust the SESSIONS_PER_USER of the profile the user is assigned to.

alter profile general_users LIMIT SESSIONS_PER_USER <num> | default | unlimited;

num = a fixed number of sessions that is the upper bound for the number of concurrent session the user can create
Default = the user is subject to the limits on those resources defined by the DEFAULT profile
unlimited = the user assigned this profile can use an unlimited amount of this resource