disable pop up asking for window credential

I wrote a web app that worked fine on my machine. however when i migrate it to the server 2008 IIS7, it kept pop up this ie window that ask for window username and password. I went into IIS 7 and allow window authentication and IE option to allow integrated window authentication but that window still popped up. and this is what i have in the web.config
<authentication mode="Windows" />
...