ORA-01017: invalid username/password; logon denied - Database Link

Error :
ORA-01017: invalid username/password; logon denied - Database Link

SQL> select * from global_name@my_link;
select * from global_name@my_link
*
ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from MY_LINK

SQL>

Above error may sometimes occur when accessing the target DB with newly created database link.

If so,try connecting to the target database via SQLPlus using the tnsnames.ora entry: sqlplus pub@tnsname

If the target db is 11g then password case sensitivity may be the issue. 

Solution:

Place the password in double quotes when you create the database link and retry.