Only one user unable to authenticate against AD using Windows Authentication on a .NET 4.0 web application on iis7

Sounds to me like the issue exists with the computer or your account. I'm hesitant to think its an issue with your account since you say ADUC works on other computers, presumably with your account.

Does the computer you try this from have a connection to the network? I would assume so, but it might not be a bad idea to do a release and renew from the command prompt. Also verify the IP settings to make sure they are valid for your network.

The computer you are trying this from, is it on the domain? If not add it then try ADUC. If it is, check the computer name and make sure an object exists for it in Active Directory. If the object exists, try removing the computer from the domain through System Properties and re-adding it to the domain after a reboot.

If none of that helps I'm bout out of ideas... I will update if I think of anything else.

Solved.

Assuming the following:

- Domain name: "domain.com"
- Group name: "Internet Users"
- User name: "UserName"
- Path to group: "domain.com\OU1\OU2\Internet Users"

The query for checking if the user is member of that group would be:

(&(memberOf=CN=Group Name,OU=OU2,OU=OU1,DC=domain,DC=com)(SAMAccountName=UserName))

So you would have to add the following to squidGuard.conf to identify the members of that group ("%s" is squidGuard.conf's placeholder for "the client's user name"):

src Internet_Users {
    ldapusersearch  ldap://dc.domain.com/DC=domain,DC=com?sAMAccountName?sub?(&(sAMAccountName=%s)(memberOf=CN=Internet Users,OU=OU2,OU=OU1,DC=domain,DC=com))
}

Caveat: it will not work if written as above, giving you a laconic "syntax error" message; this is because (part of) the statement is treated like a URL, so you have to escape special characters such as commas and whitespaces; the correct form would thus be this one:

src Internet_Users {
    ldapusersearch  ldap://dc.domain.com/DC=domain,DC=com?sAMAccountName?sub?(&(sAMAccountName=%s)(memberOf=CN=Internet%20Users%2cOU=OU2%2cOU=OU1%2cDC=domain%2cDC=com))
}

Also, in order to avoid problems with Active Directory referrals (sometimes a DC will just redirect you to another one, even if you are on the same domain it manages), it might be useful to query a global catalog:

src Internet_Users {
    ldapusersearch  ldap://gc.domain.com:3268/DC=domain,DC=com?sAMAccountName?sub?(&(sAMAccountName=%s)(memberOf=CN=Internet%20Users%2cOU=OU2%2cOU=OU1%2cDC=domain%2cDC=com))
}