symptom:
From an ASP.NET application, you may receive the following error message when accessing a remote security-enhanced resource
Login failed: unknown username or wrong password.
Solution:
1 Change the password of the ASPNET account on the Web server to password.
2 On the remote file server, change the password of the ASPNET account (create it if it does not exist) to password.
3 On the remote file server, set access permissions for the appropriate directories for the ASPNET account.
4 Modify the Web.config file and add: in the <system.web> configuration section:
<identity impersonate="true" userName="ASPNET" password="password" />
5 The passwords in the above three places can be set arbitrarily, but they must be consistent.
http://sourceforge.cnblogs.com/archive/2006/06/28/437995.html