Most Common Dbcontrol issue

You can get back to this MOS note :
EMCA fails with “SEVERE: Database instance unavailable” [ID 750697.1]

EMCA fails with Database Instance is unavailable. Fix the ORA error thrown and run EM Configuration Assistant again. [ID 1511262.1]

Creating dbconsole 11.2 fails with “Exception in thread “main” oracle.sysman.emcp.exception.DatabaseUnavailableException: Database instance unavailable” on Windows [ID 1332546.1]

Error #2:

Running EMCA fails with “SEVERE: Invalid username/password”

Solution :

1. -Make Sure You Insert Correct Password.
2. -In Some Version you can use “Password” 
3. -Recreate Password File.

You can Get back to this MOS note :
Problem: Running EMCA fails with “SEVERE: Invalid username/password” [ID 744176.1]

EMCA fails with SEVERE: Invalid username/password or database/scan listener not up or database service is not registered with scan listener. [ID 1330272.1]

Error  #3:

WARNING: ORA-01031: insufficient privileges

Solution

You need to check the logs, different error could be appear.

Failed to unlock all EM-related accounts

Alter User Identified By

Also Check MOS Notes :
Troubleshooting the ‘ORA-01031: insufficient privileges’ error when using EMCA to Create or Drop DBconsole [ID 358201.1]

Error #4:

SEVERE: Listener is not up or database service is not registered with it. Start the Listener and register database service and run EM Configuration Assistant again .

Solution :

1. – set/export ORACLE_SID
2. -Check your Listener.
3. -Check if Database Registered.

Check the below MOS note :

Troubleshooting the EMCA Error “ORA-12514” “Listener is not up. Start the Listener and run EM Configuration Assistant again” When Creating or Dropping DBConsole [ID 368591.1]

EMCA Fails With Error “ORA-12541: TNS:no listener” and “Listener is not up. Start the Listener and run EM Configuration Assistant again” [ID 975024.1]