Non-admin users cannot login

Hello.

I am starting a couple of wordpress sites: AnimeRun | Reviews and PlayMythCraft.

My problem is this: it seems every time I make an install, the first user (that I define through the site5 interface) works fine, can write posts, etc. However, when i make a new user through the default admin account, the new user cannot login, and gets a “No Data Received” error. Is this a common, fixable problem? Or is it my hosting provider’s fault?

Thank you.