Laravel 5.1 installation error (php artisan clear-compiled)

I run laravel new auth and get the following error. I'm using Windows 7 if that helps.

C:\wamp\www>laravel new auth
Crafting application...
> php -r "copy('.env.example', '.env');"
> php artisan clear-compiled

Fatal error: Call to undefined function Illuminate\Foundation\Bootstrap\mb_inter
nal_encoding() in C:\wamp\www\auth\bootstrap\cache\compiled.php on line 2117
PHP Fatal error:  Call to undefined function Illuminate\Foundation\Bootstrap\mb_
internal_encoding() in C:\wamp\www\auth\bootstrap\cache\compiled.php on line 211
7
Script php artisan clear-compiled handling the post-install-cmd event returned w
ith an error



  [RuntimeException]
  Error Output: PHP Fatal error:  Call to undefined function Illuminate\Found
  ation\Bootstrap\mb_internal_encoding() in C:\wamp\www\auth\bootstrap\cache\
  compiled.php on line 2117

via Chebli Mohamed