ASP.NET App authenticates in Firefox but not in IE

When I open my ASP.NET app in IE it asks for username and password. I enter them and it rejects them. I do the same in Firefox and it works.

Any ideas? Thanks!

I h开发者_开发技巧ave <authentication mode="Windows" />

Switch the Application Pool Identity to Network Service and it worked in both IE and Firefox. Before the Application Pool Identity was a user that was one a different domain than the domain of the user I was trying to login to the App as.