popmount

Can anyone help with some quick advice on this?

Trying to set up a multistore locally before migrating to our servers, but each time I try adding Shop2 I am unable to access it and instead receive a 500 Internal Server Error. What am I doing wrong? My main shop is located at localhost/prestashop/ and the URL that I input to add a new store is localhost/prestashop/publishers/. I've also added it under the URL localhost/publishers/ and received a 404 Not Found error. Any advice would be appreciated, I'm fairly new at working with things like this. Thanks