unable to create file

HI all, I buy a template and put the Bin directory into the root. It’s appear like www.site.com/bin because i have a site online and wanna first finish the new one. When i try to view the site everything is ok but when I go on www.site.com/bin/admin to use the admin panel, the only thing I can see is “UNABLE TO CREATE FILE ”. Which is the problem? I’m sorry for my english i am Italian. Thx all.