In Oracle 10g and before we all know that passwords are not case sensitive, so PASSWORD, Password, password would let you in and everything would be okay.
If you upgrade to Oracle 11g (I know lot of you are waiting for 11gR2), you will find that passwords are case sensitive. Here is an example of case sensitive passwords.
1 2 3 4 5 6 7
Lets try to connect with a upper case password
1 2 3 4 5 6
So what does this mean to apps running with 10g, that get ported to run with 11g. Make sure that the password set in the properties files is of the correct case.
You can also revert to 10g behavior by changing sec_case_sensitive_logon parameter to FALSE, since its TRUE by default.