There are scenarios where we face the below error while changing the password for a front end user in R12 or 11i where SSO is enabled.

Error:

Unabled to call fnd_ldap_wrapper.update_user due to the following reason:
ORA-20001: Unabled to call fnd_ldap_wrapper.update_user due to the following reason:
An unexpected error occured. Please contact System Administrator.. (USER_NAME=HSINGH)

Cause:

This may occur due to wrong SSO registration or there may be chances of duplicate entries in the FND_USER table.

Solution:

Step 1.
Delete the USER_GUID in FND_USER for each user table by running the following
SQL> set server output on
SQL> @$FND_TOP/patch/115/sql/fndssouu.sql ;
 
example
SQL> set server output on
SQL> @$FND_TOP/patch/115/sql/fndssouu.sql  USER_NAME;

2. Get the user 'USER_NAME' to log-into EBS through the SSO homepage -> this will populate FND_USER table with the same GUID from OID.
Profile level option are must to be set before the login into SSO.

Note: Make Sure System Profile "Applications SSO Auto Link User" is set to "Y" at "Site" level

If the issue persists then we might be required to  de-register and register the SSO.