From a newsgroup post: "Are you trying to have "IIS control the anonymous user password" after initially having changed it? If so, then you need to enable the password sync feature so that IIS can retrieve the IUSR password from the Security Accounts database. This is disabled in IIS v6 by default, because it constitutes a security threat. Someone able to admin IIS can have IIS run under a domain admin account, without knowing the actual admin password, and then perform tasks they would not otherwise be able to do. You can read the relevant instructions in the security chapter of the IIS 6 Resource Kit".
From a newsgroup post: "It sounds like perhaps you upgraded your machine from Win2K to Win2k3. IIS 3/4/5 used something called "subauthentication" to log on the IUSR account without actually bothering to use its password. It was able to do this because “INETINFO.exe” runs as the System account. With IIS6, they did away with “subauthentication” since the App pools no longer run as System (that is a good thing for security reasons). Probably all you need to do is edit the metabase setting to turn off the AnonymousPasswordSync option.
“adsutil.vbs set w3svc/AnonymousPasswordSync 0”
If that does not fix it, try searching for other “AnonymousPasswordSync” keys to turn off by doing: “adsutil.vbs enum_all”.
“adsutil.vbs delete <enter full path to key here>”.
Since IIS6 does not use that key, you do not need it at all actually. You could delete all instances of that key that you find if you wanted".