Error Occurs When Substring Goes Out Of Bounds?

I have an intranet application which I have been putting together with ASP.NET. I have been using VWD 2010 Beta 2 which has been fine so far. But when I go to deploy the work i've done so far to a local IIS a variable which is supposed to be; being filled with the value from HttpContext.Current.User.Identity.Name is not being filled i.e. an error occurs when substring goes out of bounds. I believe it is because the HttpContext.Current.User.Identity.Name is not putting a value into the string variable 'username'. But it is quite strange as when I run the website project within VWD 2010 it works fine without any errors. IIS is set to Integrated Windows Authentication and Annonomous Users are allowed.

public static String getName()
{
// Store username
String name = HttpContext.Current.User.Identity.Name;
// Truncate username from domain name
String[] substring = new String[1];
// Define the token at which the string will be broken at
char[] token = { '\' };
// Split the string
substring = name.Split(token);
// Return the username
return substring[1];
}

Any ideas why when running the exact same files from local IIS gives me errors?