samba - Oct 2010 - Help with sharing folder - string_to_sid error

I have a CentOS 5 box that is joined to a genuine Windows domain
controller and users can easily log into that box with their AD
credentials.   I configured the Linux box' native config files
(smb.conf, krb conf files, etc) instead of using a third-party app.

Logins work fine.

I visit the smb.conf file to try and create an smb share of a mounted
volume, and I get prompted for credentials.  No matter what I enter, I
cannot gain access.

I use my Windows box to select Start > Run \\server\share and get challenged.

The same is true from my Mac with CMD-k.

The Samba logs show string_to_sid: Sid my_ad_username does not start with
'S-'.

No amount of googling has found an answer, only many people with the same issue.

The box was recently updated via yum update -y, so all packages are up-to-date.

Any help/insights appreciated.

Thanks.

Scott