FND: Diagnostics to find the true error

After log onto EBS R12.1.3 homepage, click on Preferences and get a generic error:

You have encountered an unexpected error. Please contact the System Administrator for assistance.

The error seems just on one page, not on all pages. I had the same error message before when the database having issue, such as invalid package. But the error does not tell what is the real cause.

The key is to enable Profile option "FND: Diagnostics". After re-login, the error message will come with a link "Click here for exception details"

That leads to find the true error is an ORA-00600 error on SQL statement:

SELECT * FROM (select t.territory_short_name territory_name, t.nls_territory
from   fnd_territories_vl t, v$nls_valid_values v
where  t.nls_territory = v.value
and    v.parameter = 'TERRITORY') QRSLT  ORDER BY territory_name
;
ORA-00600: internal error code, arguments: [1350], [3], [23], [60], [AMERICAN], [0], [], [], [], [], [], []