This error just came up on my site today. No changes on server side, I checked with my hosting company. I cannot update to newer version of CMC as I get the same error.
PHP Fatal error: require_once() [<a href='function.require'>function.require</a>]: Failed opening required '__DIR__/autoloader/autoloader.php' (include_path='.;C:\php5\pear') in C:\CustomerData\webspaces\webspace_00177438\wwwroot\newgrangegold.ie\tmp\install_5485c9ef22949\libraries\compojoom\libraries\compojoom\include.php on line 18
Can you suggest anything to help further research?