Can't add new users – HELP!

Hi.

I’m a bit of WordPress noob so please bear with me…

I’ve set up and self-hosted my site https://transenduro.co.uk/transpyrenduro/

It’s up and running and I’m able to create posts and pages absolutely fine. Now I want to add a new user so my friend can also contribute to the site. This is where my problem lies – every time I attempt to add him, I get “the requested user does not exist”. My only option is to add the new user as an existing user on the network and I’m sure this is where the problem is. I don’t have the option on my dashboard to add a new user and the associated form, just the option to add an existing user…which doesn’t seem to work. In fact, having looked through several support threads, there are several options that appear to be absent from my dashboard.

I don’t (as far as I know) have any plugins running, I think it’s the standard installation of Twenty Eleven. I had problems getting the iPhone WP app to talk to the site and it turned out to be my host (NamesCo) blocking certain php files so I’m wondering if that’s it?

Confused!