functions.php line 141 error in lockout plugin

Hi,

My current configuration is:

RHEL 5.3  2.6.18-128.el5 #1 x86_64 x86_64 x86_64 GNU/Linux
httpd-2.2.3-22.el5
php-common-5.1.6-23.el5
php-cli-5.1.6-23.el5
php-5.1.6-23.el5
php-mbstring-5.1.6-23.el5
php-ldap-5.1.6-23.el5
squirrelmail-1.4.8-5.el5_2.3
---compatibility plugin Ver 2.0.14, 2009/01/01
--lockout plugin ver 1.6-1.4.1

The following is the plugin information in Squirrelmail:

Installed Plugins
    1. delete_move_next
    2. squirrelspell
    3. newmail
    4. compatibility

  Available Plugins:
    5. listcommands
    6. abook_take
    7. info
    8. message_details
    9. calendar
    10. bug_report
    11. administrator
    12. spamcop
    13. mail_fetch
    14. captcha
    15. lockout
    16. filters
    17. sent_subfolders
    18. translate
    19. fortune


If I enable the lockout plugin & try to login, the page goes blank at redirect.php.
It logs the following error in /var/log/httpd/error_log

[Fri May 15 22:05:12 2009] [error] [client 172.16.10.200] PHP Fatal error:  Call to undefined function reposition_plugin_on_hook() in /usr/share/squirrelmail/plugins/lockout/functions.php on line 141, referer: http://172.16.2.201/src/login.php

I have checked the functions.php line 141. Below is the relevant section from functions.php

function move_lockout_to_end_of_login_before_hook_do()
{

   global $PHP_SELF;
   if (stristr($PHP_SELF, '/redirect.php'))
   {
      reposition_plugin_on_hook('lockout', 'login_before', FALSE);
      reposition_plugin_on_hook('captcha', 'login_before', FALSE);
   }

}

Line 141 corresponds to:
reposition_plugin_on_hook('lockout', 'login_before', FALSE);

Unfortunately I am unable to find out what it means and how I can resolve the issue. Searched mailing lists and the web but could not find any solution.

Any help is greatly appreciated.

Thanks
--V S Rao