Oracle Error ORA-29393: user string does not exist or is not logged on

Oracle Error Message

ORA-29393: user string does not exist or is not logged on

Reason for the Error

An invalid user name was specified as argument to procedure SET_INITIAL_CONSUMER_GROUP of package DBMS_RESOURCE_MANAGER or SWITCH_CONSUMER_GROUP_FOR_USER of package DBMS_SYSTEM or the specified user was not logged on.

Solution

Specify a valid user name.