Security :: Ora-28374 Typed Master Key Not Found In Wallet

I am getting error "ora-28374 typed master key not found in wallet".

steps-

1) created tablespace and user to the respective tablespace.

2) created table by issuing command as "CREATE TABLE TEST1 (SR_NO NUMBER(3), NAME VARCHAR2(30) ENCRYPT) DEFAULT TABLESPACE ENC". (by user - enc_user)

3) Inserted rows on to the table.

4) entry made in sqlnet.ora as

ENCRYPTION_WALLET_LOCATION=
(SOURCE=(METHOD=FILE)(METHOD_DATA=
(DIRECTORY=C:appAdministratoradmin estencrypted_wallet/)))

5) issued command as sysdba - ALTER SYSTEM SET ENCRYPTION KEY IDENTIFIED BY "ASHISH123";

6) restarted the database.

7) since i want to made it autologin. so I open wallet through the below mentioned path program file >>oracle_home>> integrated management tool >> wallet But when it asked the password I typed the same password but it was not accepting. So i made new wallet with the same specified path. Also I clicked on auto login.

8) Now, i have restarted the database and tried to issue the command "ALTER SYSTEM SET ENCRYPTION KEY IDENTIFIED BY "suresh123";

While issuing the command, getting error "ora-28374 typed master key not found in wallet". "

i tried with the recreation of new folder again on the same path as -"C:appAdministratoradmin estwallet" and same entry updated on sqlnet.ora. But facing the same error.

Is there any way to re-create or modify the encryption of tablespace?