Warning: require(__DIR__/thinkphp/start.php) [function.require]: failed to open stream: No such file or directory in D:\wwwroot\xcxbuid\wwwroot\tw_admin\index.php on line 17

Fatal error: require() [function.require]: Failed opening required '__DIR__/thinkphp/start.php' (include_path='.;C:\php5\pear') in D:\wwwroot\xcxbuid\wwwroot\tw_admin\index.php on line 17

哪位大神能告诉我这是怎么回事？
我吧入口文件拿到外面也是一样，里面也是一样