Oracle9i Enterprise Edition Release 9.2.0.8.0 - Production
PL/SQL Release 9.2.0.8.0 - Production
CORE	9.2.0.8.0	Production
TNS for Linux: Version 9.2.0.8.0 - Production
NLSRTL Version 9.2.0.8.0 - Production

SQL> conn dthangad/"jillu@55"@fcdb426_mpldev1
ERROR:
ORA-12154: TNS:could not resolve service name


Warning: You are no longer connected to ORACLE.

ORA-12154: TNS:could not resolve the connect identifier specified
 *Cause:  A connection to a database or other service was requested using
 a connect identifier, and the connect identifier specified could not
 be resolved into a connect descriptor using one of the naming methods
 configured. For example, if the type of connect identifier used was a
 net service name then the net service name could not be found in a
 naming method repository, or the repository could not be
 located or reached.
 *Action:
   - If you are using local naming (TNSNAMES.ORA file):
      - Make sure that "TNSNAMES" is listed as one of the values of the
        NAMES.DIRECTORY_PATH parameter in the Oracle Net profile
        (SQLNET.ORA)
      - Verify that a TNSNAMES.ORA file exists and is in the proper
        directory and is accessible.
      - Check that the net service name used as the connect identifier
        exists in the TNSNAMES.ORA file.
      - Make sure there are no syntax errors anywhere in the TNSNAMES.ORA
        file.  Look for unmatched parentheses or stray characters. Errors
        in a TNSNAMES.ORA file may make it unusable.
   - If you are using directory naming:
      - Verify that "LDAP" is listed as one of the values of the
        NAMES.DIRETORY_PATH parameter in the Oracle Net profile
        (SQLNET.ORA).
      - Verify that the LDAP directory server is up and that it is
        accessible.
      - Verify that the net service name or database name used as the
        connect identifier is configured in the directory.
      - Verify that the default context being used is correct by
        specifying a fully qualified net service name or a full LDAP DN
        as the connect identifier
   - If you are using easy connect naming:
      - Verify that "EZCONNECT" is listed as one of the values of the
        NAMES.DIRETORY_PATH parameter in the Oracle Net profile
        (SQLNET.ORA).
      - Make sure the host, port and service name specified
        are correct.
      - Try enclosing the connect identifier in quote marks.

   See the Oracle Net Services Administrators Guide or the Oracle
   operating system specific guide for more information on naming.

SQL> conn meilvs_app/1601_ilvsd@fcdb426_mpldev1
Connected.
SQL> 
SQL> conn dthangad/"jillu@55'@fcdb426_mpldev1
ERROR:
ORA-12154: TNS:could not resolve service name


Warning: You are no longer connected to ORACLE.
SQL> 

SQL> conn meilvs_app/1601_ilvsd@fcdb426_mpldev1
Connected.
SQL> 
SQL> conn dthangad/"jillu@55"@fcdb426_mpldev1
ERROR:
ORA-12154: TNS:could not resolve service name


Warning: You are no longer connected to ORACLE.
SQL> 

SQL> create user t identified by "a@b";

User created.

SQL> grant create session to t;

Grant succeeded.

SQL> connect t/"a@b"
Connected.
SQL> connect t/"a@b"@mika
Connected.

ALTER USER dthangad IDENTIFIED BY new_pass

ALTER USER this_user IDENTIFIED BY its_new_password;