Yii提交报错 An Error occurred while handling another error:

An Error occurred while handling another error:
exception 'yii\base\InvalidRouteException' with message 'Unable to resolve the request "site/error".' in D:\mdc\YII\vendor\yiisoft\yii2\base\Module.php:532
Stack trace:
#0 D:\mdc\YII\vendor\yiisoft\yii2\web\ErrorHandler.php(97): yii\base\Module->runAction('site/error')
#1 D:\mdc\YII\vendor\yiisoft\yii2\base\ErrorHandler.php(111): yii\web\ErrorHandler->renderException(Object(yii\web\NotFoundHttpException))
#2 [internal function]: yii\base\ErrorHandler->handleException(Object(yii\web\NotFoundHttpException))
#3 {main}
Previous exception:
exception 'yii\base\InvalidRouteException' with message 'Unable to resolve the request "site/do-add".' in D:\mdc\YII\vendor\yiisoft\yii2\base\Module.php:532
Stack trace:
#0 D:\mdc\YII\vendor\yiisoft\yii2\web\Application.php(102): yii\base\Module->runAction('site/do-add', Array)
#1 D:\mdc\YII\vendor\yiisoft\yii2\base\Application.php(380): yii\web\Application->handleRequest(Object(yii\web\Request))
#2 D:\mdc\YII\frontend\web\index.php(17): yii\base\Application->run()
#3 {main}

Next exception 'yii\web\NotFoundHttpException' with message 'Page not found.' in D:\mdc\YII\vendor\yiisoft\yii2\web\Application.php:114
Stack trace:
#0 D:\mdc\YII\vendor\yiisoft\yii2\base\Application.php(380): yii\web\Application->handleRequest(Object(yii\web\Request))
#1 D:\mdc\YII\frontend\web\index.php(17): yii\base\Application->run()
#2 {main}

namespace frontend\Controllers;//命名空间才能加载一些类

改为controllers;小写