When you try to join a Windows Vista-based client computer to a Microsoft Windows NT 4.0 domain, you may receive the following error message:

The following error occurred attempting to join the domain domainname:
Logon failure: unknown user name or bad password

When this problem occurs, the following error may appear in the %windir%\Debug\Netsetup.log file:

NetUseAdd to \\DC01\IPC$ returned 1326
NetpJoinDomain: status of connecting to dc ‘\\DC01′: 0×52e
NetpDoDomainJoin: status: 0×52e

Note: Error code 1326 and error code 0×52e are both mapped to the ERROR_LOGON_FAILURE error. The ERROR_LOGON_FAILURE error corresponds to the following error message:

Logon failure: unknown user name or bad password.

This problem also applies to Windows Server 2008.