ORA-1017: invalid username/password when creating database link
If you are getting a "ORA-1017: invalid username/password; logon denied" when creating a database link, and you ensured to enter the correct password, you probably try it against a 11g database version. In this version is a new feature the "case sensitivity rules". This statement worked from a 11g db to a 10g database, and threw a exception from 10g to 11g.
create public database link testdblink connect to TESTUSER identified by 'testpw' using 'test2db';
After using double-quotes it worked fine in every direction.
create public database link testdblink connect to TESTUSER identified by "testpw" using 'test2db';