IIS or Sharepoint authentication failure

I'm not sure if this is an IIS or Sharepoint issue but I really need some
help as I can reproduce the problem but have been unable to fix this.

We have a Novell Network and an Active Directory network. We sync accounts
from Novell to AD. AD is used to authenticate a Solomon Business Portal web
site, which resides on Sharepoint. I have Basic Authentication setup and the
site is configured for SSL.

Most users have had no problems logging in. They can change their Novell
password and then they log in to Business Portal and their new password
works. I have seen intermittent problems where a password change will not
allow the user to log in to Business Portal. I can, however, log in to the
domain as the user from a laptop that is a member of the domain.

So where could the failure be occuring? I've done IIS traces and the
summary file says that Basic Logon Failed. Is there any way to trace a
Windows logon to a domain? I know you can do auditing for Success and
Failures but that isn't helping me to troubleshoot. Could this be a caching
issue? I don't have caching enabled anywhere that I am aware of. I've
checked Registry settings to verify that.

Here are steps I just took with a user account

1 - Business Portal Logon fails (401.1 error)
2 - Reset user password in AD
3 - Business Portal Logon works
4 - Deleted user account in AD
5 - Resynched user account from Novell
6 - Business Portal Logon fails (401.1 error)
7 - Log on to AD Domain from a laptop as the user - success (so the AD
password is valid and the LDAP sync with Novell works)
8 - Business Portal Logon fails (Sharepoint error - Access denied. You do
not have permission to perform this action or access this resource.


Access requests are not enabled.)
9 - Recreate Business Portal account
10 - Business Portal Logon works