Could this problem be related to 0007948 and/or 0005591 ?

I tried the suggestion in
http://www.mantisbt.org/bugs/view.php?id=7948,
Nothing happened for old users, for old users I got a query failed error.

I am not 100% sure how to proceed for debugging this; probably you could try to enable query tracking and report here exactly WHICH one is failing. Please add to your config_inc.php the lines:

$g_show_queries_list = ON;
$g_show_detailed_errors = ON;
$g_display_errors = array(
E_WARNING => 'halt',
E_NOTICE => 'halt',
E_USER_ERROR => 'halt',
E_USER_WARNING => 'halt',
E_USER_NOTICE => 'halt'
);

and report here the error(s) you see.

Here is the errors I got after enabling debugging:

Database query failed. Error received from database was 0001064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '102' at line 4 for the query: SELECT *
FROM mantis_bugnote_table
WHERE bug_id='1'
ORDER BY date_submitted 102

Please use the "Back" button in your web browser to return to the previous page. There you can correct whatever problems were identified in this error or select another action. You can also click an option from the menu bar to go directly to a new section.

Full path: /var/www/html/mantis/core/database_api.php
Line: 128
The query traceback screenshot is attached.

ahhh wait.

Your setting:

$g_bugnote_order = DESC;

is not right. it should be:

$g_bugnote_order = 'DESC';

I tried the following settings
$g_default_bugnote_order = 'DESC';

$g_bugnote_order = 'DESC';

But same error.

Ok. please test this;

1. set:

   $g_default_bugnote_order = 'DESC';
   $g_bugnote_order = 'DESC';

2. create a new user

3. login with this new user and verify if you still get errors.

It worked for new users. But for the old users the sort order remains the same. However there are no errors. Thanks for guiding me.

Ok. so I know where the "problem" in the code is...

About your other users, tell them to try going in "My Account", then "Preferences" and change their "Notes Sort Order" there.

I have already intimated them. Thanks.

Ok. I commited a change that will hopefully avoid other issues like this.
In case it was not clear, the problem is that DESC was also a constant defined in constants_inc.php, so that, though we expect a string to be used for the default bugnote order, no error was reported.