I am getting this error While tring to connect the Database first time.
My DB details are:-
Oracle Release 18.104.22.168.0.
Existing charater set - WE8ISO8859P1
new charater set - AL32UTF8
OS -RHEL 6.2 64 bit.
Error Message in Detailes:-
The Database Migration Assistant for Unicode requires that Oracle XDB component is installed in the database. The DBA_REGISTRY view should contain one row with the column COMP_ID equal to 'XDB' and the column STATUS equal to 'VALID'.
Refer to the Oracle XML DB Developer's Guide for instructions on how to install the missing component.
Looking at your post you are trying to use the Database Migration Assistant. For the action you are trying to complete you will need the XML DB components installed and DMA is thinking that you do not have this installed.
Solution, install the needed functionality and retry.