I have just installed SilverStripe on my site and it appeared to install just fine. However, when I try to add new users, the pop-up window loads an error page (http://oermops.perfectz.info/silver/sapphire/thirdparty/greybox/loader_frame.html). I have tried to install SilverStripe in the root of my site and in a separate directory... same result. I have checked and loader_frame is on the server. I see no reason why I am getting an error!
I would also like people to use usernames rather than email address to log into the site.
Does the file exist & have the correct permissions set on it and its parent folders?
Also, you don't have to use e-mail addresses to create member logins. The email field will accept both email and usernames. It's just a matter of labeling the field. On Regal Models' model websites, we do this by relabeling the email field "Username" and it works either way.