HTTP Error 500 /panel url

Hello, i have clone the starterkit into my root folder, and i have create a server whit php -S all works fine, but when i go to the /panel Url, it shows me the HTTP Error 500.
How can i fix this?.

My Solution

i have install the mbstring extension whit sudo apt-get install php7.0-mbstring and after that i reload my apache server whit sudo service apache2 restart

More information about the mbstring extension