Enterprise Manager 11g fails database instance unavailable

In Oracle 11g RAC the enterprise manager dbconsole doesn't start and gives an OC4J not available error.
If we try to deconfig using emca as below we receive an error database instance unavailable. If you face the same issue then here is one of the possible solution

export ORACLE_SID to the instance id not db id for example if your 2 node rac db is orcl then instance will be orcl1 & orcl2.

Set the ORACLE_SID to orcl2 and export the oracle sid

Go to oracle_home/bin directory and check the emca and emctl files and update if required for the ORACLE_HOME & ORACLE_SID.

And then execute the below command to remove the EM repository


[oracle@home bin]$ emca -deconfig dbcontrol db -repos drop

STARTED EMCA at May 2, 2012 11:17:49 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: orcl1
Listener port number: 1521
Password for SYS user:
Password for SYSMAN user:

Do you wish to continue? [yes(Y)/no(N)]: Y
May 2, 2012 11:18:03 AM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at /opt/oracle/cfgtoollogs/emca/racdb/emca_2012_05_02_11_17_49.log.
May 2, 2012 11:18:03 AM oracle.sysman.emcp.EMDBPreConfig performDeconfiguration
WARNING: EM is not configured for this database. No EM-specific actions can be performed.
May 2, 2012 11:18:06 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Dropping the EM repository (this may take a while) ...

And after dropping recreate the repository.