Sharepoint 2007 MOSS with AD imported users. All servers are 2008.

I have around 50 users, over the past 2 months, I have had a handful of the users suddenly unable to login to Sharepoint. When they login, they either get a blank screen or they are repropmted. These users are using accounts that have been used for many months, sometimes the problem originates with a password change. In all cases, the users account works on every other Active Directory authenticated resource (domain, exchange, LDAP).

In the most recent case, last night I was forced deleted a user ("John smith") because of corruption. The orifinal account name was jsmith. I deleted him from active directory, then deleted him from the profile list in Sharepoint Shared Services. I could not find a way to delete him from the Sharepoint user list, but I reran the import after recreating his account (renamed it too just to be sure to "smithj"). At first, this did not wor, the user could still access all other resources but Sharepoint. then, some 30 minutes later it inexplicably started working.

This morning, the user changed passwords, which immediatly broke the login on Sharepoint again.

I am at a loss on how to troubleshoot this.