>I have a Web site application. It is defined to use a connection string to SQL Server with Integrated Security=True. The IIS of that virtual directory is set to an application pool. That application pool is used for other Web site. It works. The application is set to use a specific username.
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>However, on the new Web site, when I try to do a SQL Server command, I get:
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>Login failed for user 'NT AUTHORITY\IUSR'.
>
>I cannot understand why that Web site is trying to use that account when the application pool is set for a specific user.
>
>Anyone would have an idea what could be a factor here?

What version of IIS ?

Are you sure that the new site is pointed to the correct application pool. The default behaviour in IIS7 when creating a new site is to create an additional app pool of the same name using the ApplicationPoolIdentity identity. You may need to change the Application Pool in the site advanced settings.