With one of my websites, logging in the first time just sends the user straight back to the login form. There is no error message. The second login attempt works fine. This only happens on the live (public) server; the test server behaves the way that it should.
Has anyone encountered this before? If so, any idea what would trigger this? I've had problems in the past that were caused due to the live server having mod_security installed (it's a shared hosting server, so the configuration isn't set by me), so I'm guessing that a server-specific setting is responsible.
One other wierd thing is that the dev/build output is unformatted on the live server. It just comes out as a mass of unformatted text. Once again, the test server doesn't do this.