Oracle 11g Enterprise Manager is not able to connect to the database instance.

When you try to open EM you may see following message "Enterprise Manager is not able to connect to the database instance. The state of the components are listed below."

Authentication passed but it does not work.

If problem on authentication check sysman user`s account status.

SQL> select account_status from dba_users where username='SYSMAN';

Also it will helpful checking emctl`s log which locates under:

/u01/app/oracle/product/11.2.0/dbhome_1/localhost.localdomain_ulfetdb/sysman/log

After checking logs I decided to recreate dbcontrol using below command.

It will ask some parameters (some of them optional, just enter and skip)
Also to be patient, it may last several minutes...

[oracle@localhost ~]$ emca -config dbcontrol db -repos recreate

STARTED EMCA at Dec 26, 2012 10:19:51 AM
EM Configuration Assistant, Version 11.2.0.0.2 Production
Copyright (c) 2003, 2005, Oracle. All rights reserved.

Enter the following information:
Database SID: ulfetdb
Database Control is already configured for the database ulfetdb
You have chosen to configure Database Control for managing the database ulfetdb
This will remove the existing configuration and the default settings and perform a fresh configuration
Do you wish to continue? [yes(Y)/no(N)]: yes
Listener ORACLE_HOME [ /u01/app/oracle/product/11.2.0/dbhome_1 ]: listener
Password for SYS user:
Password for DBSNMP user:
Password for SYSMAN user:
Password for SYSMAN user: Email address for notifications (optional):
Outgoing Mail (SMTP) server for notifications (optional):
-----------------------------------------------------------------

You have specified the following settings

Database ORACLE_HOME ................ /u01/app/oracle/product/11.2.0/dbhome_1

Local hostname ................ localhost.localdomain
Listener ORACLE_HOME ................ listener
Listener port number ................ 1521
Database SID ................ ulfetdb
Email address for notifications ...............
Outgoing Mail (SMTP) server for notifications ...............

-----------------------------------------------------------------
Do you wish to continue? [yes(Y)/no(N)]: yes
Dec 26, 2012 10:21:01 AM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at /u01/app/oracle/cfgtoollogs/emca/ulfetdb/emca_2012_12_26_10_19_50.log.
Dec 26, 2012 10:21:02 AM oracle.sysman.emcp.util.DBControlUtil stopOMS
INFO: Stopping Database Control (this may take a while) ...
Dec 26, 2012 10:21:25 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Dropping the EM repository (this may take a while) ...
Dec 26, 2012 10:28:38 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully dropped
Dec 26, 2012 10:28:39 AM oracle.sysman.emcp.EMReposConfig createRepository
INFO: Creating the EM repository (this may take a while) ...
Dec 26, 2012 10:43:01 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully created
Dec 26, 2012 10:43:30 AM oracle.sysman.emcp.EMReposConfig uploadConfigDataToRepository
INFO: Uploading configuration data to EM repository (this may take a while) ...
Dec 26, 2012 10:45:19 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Uploaded configuration data successfully
Dec 26, 2012 10:45:20 AM oracle.sysman.emcp.ParamsManager getLocalListener
WARNING: Error retrieving listener for localhost.localdomain
Dec 26, 2012 10:45:30 AM oracle.sysman.emcp.util.DBControlUtil configureSoftwareLib
INFO: Software library configured successfully.
Dec 26, 2012 10:45:30 AM oracle.sysman.emcp.EMDBPostConfig configureSoftwareLibrary
INFO: Deploying Provisioning archives ...
Dec 26, 2012 10:46:14 AM oracle.sysman.emcp.EMDBPostConfig configureSoftwareLibrary
INFO: Provisioning archives deployed successfully.
Dec 26, 2012 10:46:14 AM oracle.sysman.emcp.util.DBControlUtil secureDBConsole
INFO: Securing Database Control (this may take a while) ...
Dec 26, 2012 10:46:52 AM oracle.sysman.emcp.util.DBControlUtil secureDBConsole
INFO: Database Control secured successfully.
Dec 26, 2012 10:46:52 AM oracle.sysman.emcp.util.DBControlUtil startOMS
INFO: Starting Database Control (this may take a while) ...
Dec 26, 2012 10:48:42 AM oracle.sysman.emcp.EMDBPostConfig performConfiguration
INFO: Database Control started successfully
Dec 26, 2012 10:48:42 AM oracle.sysman.emcp.EMDBPostConfig performConfiguration
INFO: >>>>>>>>>>> The Database Control URL is https://localhost.localdomain:1158/em <<<<<<<<<<<
Dec 26, 2012 10:48:49 AM oracle.sysman.emcp.EMDBPostConfig invoke
WARNING:
************************ WARNING ************************

Management Repository has been placed in secure mode wherein Enterprise Manager data will be encrypted. The encryption key has been placed in the file: /u01/app/oracle/product/11.2.0/dbhome_1/localhost.localdomain_ulfetdb/sysman/config/emkey.ora. Please ensure this file is backed up as the encrypted data will become unusable if this file is lost.

***********************************************************
Enterprise Manager configuration completed successfully
FINISHED EMCA at Dec 26, 2012 10:48:49 AM

Let`s check

Alternatively you can directly drop repository and then create it again using below commands.

emca -deconfig dbcontrol db -repos drop
emca -config dbcontrol db -repos create

I hope this article helped you. Your suggestions/feedback are most welcome.

Keep learning... Have a great day!!!