Determine if DC is available for Offline work question

[Anthony Yott]

We are currently using SSPI to authenticate our users to the domain (see
http://support.microsoft.com/default.aspx?scid=kb;EN-US;180548) in our
application. We can't use LogonUser because we have to support Win 2000.

We need to be able to determine if the domain controller(s) is unavailable
(ie either the client's network cable is unplugged or they are not logged
into the domain). In the SSPI code we have code to check the last error
(e.g.. GetLastError) if the call fails. When testing this code, my co-worker
gets the following message when his network cable is unplugged:

“There are currently no logon servers available to service the logon
request.†DWORD = 0x0000051f

However when I unplug my cable I get a different error as follows:

“Logon failure: unknown user name or bad password.†DWORD = 0x0000052E

We are both using Win XP SP2.

Can anyone offer an opinion as to why there is a difference or is there a
"best practice" for determining whether I can reach the domain server(s)?

Any help here would be greatly appreciated.

Thanks in advance,