页面被要求两次

I'm having a trouble with my CodeIgniter site. I notice everytime I go to a page, the page is requested twice by the browser (Tried on Firefox and Chrome and different computers too). Here's a screenshot from Firebug: enter image description here

As you can see in the image, the page invite is requested twice. I've looked at Chrome developer tools and it says that the second request is initiated from line 4 of the file jquery-1.7.1.min.js. Also, in Chrome developer tools, the second request has the same size as the first one. Yet, the response is actually empty (Same thing with Firebug). A simple Hello World PHP page still works fine though.

What could've been the cause of this problem?

You probably have a resource requested during page load which erroneously has an almost-empty URL. For example, in your CSS you may have background-image: url(#), or an ajax call to "#". Notice that the second URL is invite#, not invite. That's a clue.