Switching to the oracle user shows the following error messages,

Issue 1 :
-------------
su: incorrect password

Solution :
------------
passwd -u oracle -------------This will unlock the user account on behalf of expiration.
vi /etc/passwd  -> remove "x" for the oracle user.
vi /etc/group   -> remove "x" for the dba group.

Issue 2 :
----------
#passwd user
Authentication Token Manipulation Error
#

Solution :
------------
root@ebs # pwconv

Description about this error :
--------------------------------------
This error is being produced because you are using shadowed password files and the shadow doesn’t have entry for this user. i.e, /etc/passwd has an entry for this user, but /etc/shadow doesn’t.
In order to resolve this, you can either add the entry manually or recreate the shadow file. You can use pwconv to recreate the shadow file. See the manpage for more details on this.