Database connection Error

Hi,
I have a web application  where I am connecting database through webservice. From Webapp I am passing Connectionstring and webservice connect to database return dataset.
In my system the app works fine. When I am deploying in IIS server, It is giving error.
"Login failed. The login is from an untrusted domain and cannot be used with Windows authentication."
In my web.config I have already set
 <authentication mode="Windows"/>
      <identity impersonate="true" userName="" password=""/>
      <authorization>
        <allow users="*"/>
      </authorization>
 
Thanks,
Viki 
 
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