Need mapping?

I’m having trouble installing to my domain – followed the steps but I keep getting errors when finally doing the domain.com/wp-admin/install.php.

When I had the domain mapped (I had purchased that ages ago thinking it was necessary – is it?), it just says “file not found” on my page.

When I delete the domain mapping, it says “Warning! Domain mapping upgrade for this domain not found. Please log in and go to the Domains Upgrades page of your blog to use this domain. “

Do I need it mapped or not?