failed bucket zend/loader.php. perplexing work out why?

i have hereditary fan site crashes each 3 4 days. built controlling zend-framework i have knowledge.

the following code:

<?php
    // certain classes consolidate path.
   ini_set('include_path', ini_get('include_path') . path_separator . 'lib' . path_separator . 'app' . directory_separator . 'classes');

    // autoload consolidate need statements needed.
    require_once 'zend/loader.php';
    zend_loader::registerautoload();

    // run application.
    app_main::run('production');

is causing following error:

[tue sep 02 12:58:45 2008] [error] [client 78.***.***.32] php warning: require_once(zend/loader.php) [function.require-once]: unsuccessful open stream: such record office /srv/www/vhosts/example.co.uk/httpdocs/bootstrap.php line 6 
[tue sep 02 12:58:45 2008] [error] [client 78.***.***.32] php lethal error: require_once() [function.require]: unsuccessful opening mandatory 'zend/loader.php' (include_path='.:.:/usr/share/php5:/usr/share/php5/pear') /srv/www/vhosts/example.co.uk/httpdocs/bootstrap.php line 6 

i don't even know where start perplexing repair this. turn trust php middle nonetheless i said, i have trust zend. also, contacting uncanny developer an option.

the engaging thing even nonetheless formula run each page site strike blunder wholly duty each then.

i trust contingency something include_path nonetheless i am sure.