We have a website with Windows Authentication. We have the AD group defined in the web.config who can access the website. Some users in the AD group are able to login to the application. However, some other users are getting a prompt for credentials, but not able to login. What could be the reason for this behavior? How do we correct it?

Sample Structure of the config setting is:

```
<appSettings>
    <add key="Group1" value="XXX\AppleFruit.Red" />
</appSettings>

```

Note: The website is hosted in IIS7