Warning: require_once(OS/Guess.php) [function.require-once]: failed to open stream: No such file or directory in D:\PHP\5.2\PEAR\Installer.php on line 23

Fatal error: require_once() [function.require]: Failed opening required 'OS/Guess.php' (include_path='.;D:\PHP\5.2\pear') in D:\PHP\5.2\PEAR\Installer.php on line 23