401.1 Errors for some users accessing secured site

[DomPedro]

I've recently had to move our secured website from UNIX to NT using IIS 4. Initially only Windows Challenge/Response was enabled and many users were in and working fine, but some got 401.2 errors. I found that basic authentication was needed as some proxies don't like NTLM, and all users now have log on locally rights, and I can login from a machine on the local intranet using their username and password, but there are now a few users complaining of 401.1 errors, while most can get in.

One user experiencing the errors over the internet can get in via Netscape but not IE, while another can't get in from his office desktop, but can from his dial-up ISP connection. The logfile shows a "-" where their user should be and all users are setup identically on the NT server.

Our IS people can't help, and all the users say it can't be there proxies as they can access other secured sites. Anyone know of a possible cause or solution ?

 

[DomPedro]

More info on this issue.
Things tested that have had no effect :
1. Setting browsers to use HTTP 1.1 through proxy.
2. Putting the machine name (local domain) in the DOMAIN dialogue on the login prompt.
3. Giving user Access this computer from network user rights in addition to the log on locally that Basic Authentication requires.
Another user has confirmed that they can access my site via dial-up ISP rather than their remote office network, so this has to be something that their proxy server is doing doesn't it ?
Any help is appreciated.