Firebug NET Tabs give intermittent 500 server error in admin - Joomla! Forum - community, help and support

the error appear when joomla administration on , repeat @ regular interval without real fuss.
see image —this net tab of firebug

head-administrator.jpg

always follow php errors logs

code: select all

[15-aug-2012 17:54:10] php warning:  require_once(/applications/mamp/htdocs/path-to/administrator) [<a href='function.require-once'>function.require-once</a>]: failed open stream: unknown error: 0 in /applications/mamp/htdocs/path-to/administrator/components/com_cpanel/admin.cpanel.php on line 17

[15-aug-2012 17:54:10] php fatal error:  require_once() [<a href='function.require'>function.require</a>]: failed opening required '' (include_path='.:/applications/mamp/bin/php5.3/lib/php') in /applications/mamp/htdocs/path-to/administrator/components/com_cpanel/admin.cpanel.php on line 17


i have few site generating same errors...


i really, really, appreciate hints can me in there...

[b]i need solve this