You ran into a security issue. First, you have to disable anonymous access to your webapplication in IIS and set identity to impersonate='true' in your web.config. This way you won't access the filesystem as the aspnet user but as the logged on user. Second, the ability to access a remote machine depends on the type of logon session created. And the type of logon session created depends on the type of authentication you configured (in IIS). When specifing 'Windows Integrated' a network loggon session will be created, which has no network credentials and won't be able to acccess a remote machine. (The only way to make this work is to make use of delegation.) When configuring 'Basic Authentication' an interactive logon session is created, which has network credentials, and will be able to access a remote machine. When your workstation is the same as your IIS box it will always work because your (interactive) logon session will be used to authenticate.

When you use Windows Explorer to browse a remote machine's filesystem your interactive loggon session will be used to authenticate with that machine.