oracle error- ORA-00027: cannot kill current session

ORA-00027:  cannot kill current session

Cause:     Attempted to use ALTER SYSTEM KILL SESSION to kill the current session.

Action:     None.

oracle error- ORA-00026: missing or invalid session ID

ORA-00026:  missing or invalid session ID

Cause:     Missing or invalid session ID string for ALTER SYSTEM KILL SESSION.

Action:     Retry with a valid session ID.

oracle error- ORA-00025: failed to allocate string

ORA-00025:  failed to allocate string

Cause:     Out of memory.

Action:     Restart with larger sga heap.