Error occur after composer require - yii2

Question

I ran composer require 2amigos/yii2-multi-select-widget "*" and after my site went down
An Error occurred while handling another error:
yii\base\InvalidArgumentException: Invalid path alias: #dektrium/rbac/views in C:\xampp\htdocs\webster\vendor\yiisoft\yii2\BaseYii.php:154
Stack trace:
#0 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\Theme.php(144): yii\BaseYii::getAlias('#dektrium/rbac/...')
#1 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\View.php(228): yii\base\Theme->applyTo('C:\\xampp\\htdocs...')
#2 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\web\ErrorHandler.php(266): yii\base\View->renderFile('C:\\xampp\\htdocs...', Array, Object(yii\web\ErrorHandler))
#3 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\web\ErrorHandler.php(126): yii\web\ErrorHandler->renderFile('#yii/views/erro...', Array)
#4 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\ErrorHandler.php(111): yii\web\ErrorHandler->renderException(Object(yii\base\InvalidArgumentException))
#5 [internal function]: yii\base\ErrorHandler->handleException(Object(yii\base\InvalidArgumentException))
#6 {main}
Previous exception:
yii\base\InvalidArgumentException: Invalid path alias: #dektrium/rbac/views in C:\xampp\htdocs\webster\vendor\yiisoft\yii2\BaseYii.php:154
Stack trace:
#0 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\Theme.php(144): yii\BaseYii::getAlias('#dektrium/rbac/...')
#1 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\View.php(228): yii\base\Theme->applyTo('C:\\xampp\\htdocs...')
#2 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\View.php(156): yii\base\View->renderFile('C:\\xampp\\htdocs...', Array, Object(backend\controllers\SiteController))
#3 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\Controller.php(384): yii\base\View->render('index', Array, Object(backend\controllers\SiteController))
#4 C:\xampp\htdocs\webster\backend\controllers\SiteController.php(65): yii\base\Controller->render('index')
#5 [internal function]: backend\controllers\SiteController->actionIndex()
#6 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\InlineAction.php(57): call_user_func_array(Array, Array)
#7 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\Controller.php(157): yii\base\InlineAction->runWithParams(Array)
#8 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\Module.php(528): yii\base\Controller->runAction('', Array)
#9 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\web\Application.php(103): yii\base\Module->runAction('', Array)
#10 C:\xampp\htdocs\webster\vendor\yiisoft\yii2\base\Application.php(386): yii\web\Application->handleRequest(Object(yii\web\Request))
#11 C:\xampp\htdocs\webster\backend\web\index.php(18): yii\base\Application->run()
#12 {main}
It is all that I did. Nothing more nothing less. Just tried to install multi-select and my site went down. Why is that? What can cause this? I tried to remove it composer remove 2amigos/yii2-multi-select-widget and nothing happen. I am totally shocked. Please give me advice!