Error when using PrincipalContext.ValidateCredentials to authenticate against a Local Machine?

Question

I have a WCF service which contains a Login method that validates a username and password against the local machine credentials, and after a seemingly random period

Answer 1

The closest I can find online towards explaining this problem is this forum post, where the user experiencing the same error and got a replay stating:

The WinNT provider does not do well in a server environment. I am actually suprised you don't see this with a much smaller load. I have been able to get this with only 2 or 3 users.

and this SO comment stating

The BEST way to correctly authenticate someone is to use LogonUserAPI as @stephbu write. All other methods described in this post will NOT WORK 100%

where "all other methods" includes the top voted answer of using PrincipalContext.ValidateCredentials

Its sounding like PrincipalContext.ValidateCredentials isn't completely 100% reliable on Windows Server 2003 and IIS6.0, so I rewrote my authentication code to use the LogonUser WinAPI method instead.

[DllImport("advapi32.dll", SetLastError = true)]
public static extern bool LogonUser(
    string lpszUsername,
    string lpszDomain,
    string lpszPassword,
    int dwLogonType,
    int dwLogonProvider,
    out IntPtr phToken
    );

IntPtr hToken;
if (LogonUser(username, "", password, 
    LOGON32_LOGON_NETWORK, LOGON32_PROVIDER_DEFAULT, out hToken))
{
    ...
}