ORA-20000

I got an error:OpenService failed - The specified service does not exist as an installed service.

C:\app\product\11.2.0\client_2\bin>schagent.exe -registerdatabase dbag 8080
Agent Registration Password ? *******************
*
Oracle Scheduler Agent Registration for 11.2 Agent
Agent Registration Successful!

C:\app\product\11.2.0\client_2\bin>schagent.exe -unregisterdatabase dbag 8080

1] dbag

Enter the number of the database being unregistered or 0 to cancel:
1
Oracle Scheduler Agent Unregistration for 11.1 Agent
Agent Unregistration Failed!
Error: ORA-27452: 192 is an invalid name for a database object.

C:\app\product\11.2.0\client_2\bin>schagent.exe -unregisterdatabase dbag 8080
No registered database v11.2 or higher to be unregistered.

C:\app\product\11.2.0\client_2\bin>schagent.exe -removeagentservice
OpenService failed - The specified service does not exist as an installed service. (0x424)

SQL> select * from all_scheduler_external_dests;

DESTINATION_NAME  HOSTNAME           PORT IP_ADDRESS       ENABLED COMMENTS
----------------- ---------------- ------ ---------------- ------- ---------------------------------------------------------
AGENT_1           192.168.100.102   65001 192.168.100.102  TRUE    Registered on 30-JAN-14 11.06.31.426000 AM EUROPE/MOSCOW

SQL> 

begin
  dbms_scheduler.drop_agent_destination(destination_name => 'AGENT_1');
end;

SQL> 

Remove windows service:

C:\app\product\11.2.0\client_2\bin>sc delete OraClient11g_home2_OracleSchedulerExecutionAgent
[SC] DeleteService SUCCESS

Use function dbms_isched.get_credential_password:

SQL> 
SQL> begin
  2    dbms_scheduler.create_credential(credential_name => 'credential4test',
  3                                     username        => 'user4test',
  4                                     password        => 'pass4test');
  5  end;
  6  /
 
PL/SQL procedure successfully completed
 
SQL> 
SQL> select user$.name as credential_owner,
  2         obj$.name  as credential_name,
  3         scheduler$_credential.username,
  4         scheduler$_credential.password,
  5         dbms_isched.get_credential_password(obj$.name, user$.name) enc_password
  6  from   scheduler$_credential,
  7         obj$,
  8         user$
  9  where  user$.user# = obj$.owner# and
 10         scheduler$_credential.obj# = obj$.obj#;
 
CREDENTIAL_OWNER   CREDENTIAL_NAME  USERNAME     PASSWORD                                ENC_PASSWORD
------------------ ---------------- ------------ --------------------------------------- --------------
SYS                CREDENTIAL4TEST  user4test    BUG19SWE76fBKqdqgKsZu/fTpM8wOfSQXg==    pass4test

SQL>