Running The Project Versus Viewing In IIS

This could be a simple one but it has got me baffled. I have a ASP.NET solution that I have stored in C/inetpub/www/root/website. The solution and project files are all stored in there and I have set it up as a virtual directory in IIS.so I can view the web page in 2 ways.

1. - By running the solution [URL]

2. - By viewing the url in IE: [URL]

I changed the project to use windows authentication and I added alabel in the top right of the page which displays the user logged in i.e. DOMAINusername.

When I run the solution from VS2008 it displays the username on the page no problem (that is my logon id since I am running it). But when I view the page by typing the URL into IE - it doesnt seem to recognise the authentication and it doesnt display my DOMAINusername in the label.

Any ideas why this is? I thought maybe it was something to do with the .dlls but I did a simple test. In the project I created a new a label on the page and in the page_load I wrote "label.text = "Test Text". In both cases the label showed "Test Text" as expected so it is nothing to do with building the solution. Is there something about windows authentication - why would it work in one case and not in the other? So as a third test I actually opened IIS and right-clicked on the my website in the console and choose "browse".

I then got the following error:

Sequence contains no elements

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: Sequence contains no elements

Source Error:

[Code]....

Now I set a break point at this point in my project in VS2008 - but when I run it there it doesnt even go to this code!