If SSO Integration in Place you cannot change the password from System Administrator, User Management, FND_USER_PKG

ORA-20001: APP-FND-02602: Unabled to change password for user [username] for this following reason:
This password is not managed by Oracle Applications so it can not be changed here..
ORA-06512: "APPS.APP_EXCEPTION", at line 72
ORA-06512: "APPS.FND_USER_PKG", at line 322
ORA-06512: "APPS.FND_USER_PKG", at line 1147
ORA-06512: at line 1

This error occurs if you have both SSO-enabled E Business Suite (EBS) and are trying to use the OIM E Business Suite User Management connector to manage passwords in EBS. If you SSO-enable an EBS user, then their password is no longer stored in EBS, rather, it is stored in OID / SSO. As a result, EBS refuses to allow OIM to update the password.

You cannot use the OIM E Business Suite User Management connector to manage passwords for SSO-enabled EBS users. You need to choose one of the following:
1. Do not use the Update Password feature of OIM EBS User Management connector, or
2. not to SSO enable E Business Suite 

Change the %Application%SSO% Profile Options:
Application SSO LDAP Synchronization
Application SSO Login Types