ORA-28001: the password has expired (DBD ERROR: OCISessionBegin).

A. Verify if the password is expired.
 1.select username,ACCOUNT_STATUS,EXPIRY_DATE from dba_users where username='DBSNMP';

USERNAME                       ACCOUNT_STATUS                   EXPIRY_DA
------------------------------ -------------------------------- ---------
DBSNMP                         EXPIRED                                             19-DEC-10

B. If the password is expired and you don’t have the password then take the encrypted password using the below query.

 2.SQL> select PASSWORD from dba_users where username='DBSNMP';


 PASSWORD
 ------------------------------
 46169788712239BD

C. Check the profile value for that user .
3. SQL> select PROFILE from dba_users where username='DBSNMP';

PROFILE
------------------------------
APP_QUERY


D. Change the profile value to default temporarily.

4. SQL> alter user DBSNMP PROFILE default;
User altered.

E. Verify if the change is reflected.

5. SQL> select PROFILE from dba_users where username='DBSNMP';
PROFILE
------------------------------
DEFAULT

F. Reset the password using the below command to its old password as in step 2.
6. SQL> alter user DBSNMP identified by values '46169788712239BD';
User altered.

G. Now check if the account is open.
7. SQL> select username,ACCOUNT_STATUS,EXPIRY_DATE from dba_users where username='DBSNMP';
USERNAME                       ACCOUNT_STATUS                   EXPIRY_DA
------------------------------ -------------------------------- ---------
DBSNMP                         OPEN
H. Reset the profile value back to its original as in step 3.

8. SQL> alter user DBSNMP PROFILE APP_QUERY;
User altered.

I. Verify if the change has been reflected and it is the same as it was earlier.
9. SQL> select PROFILE from dba_users where username='DBSNMP';
PROFILE
------------------------------
APP_QUERY
**************   DONE   **************