hi,
are you using domain or workhroup ?
are you using Kerberos (dafult) or NTLM authentication ?
if are using Kerberos:
on Web Browser try to add your website address to "trusted sites"; after set on security "local intranet\user authentication" option: "user authentication with automatic logon on intranet".
-> now can can use your network kerberos ticket to open webservice page