I have recently updated a portal to 4.8.2.  One problem that seemed to occur in 3.3.5 with old auth was an occasional corruption of an account that would rise the below message.  Now the problem is more frequent and considering I updated Monday, I suspect it will be more frequent than tolerable.  I cannot discern yet if the problem is from our network group policies on IE security settings or some problem with the auth module.  I do know that if you delete the users account, the problem goes away temporarily.  I also know if you open a browser and attempt to get to the child portal; this error appears on the first attempt.  The second attempt in the same browser session opens the site but does not auto-login the user.

Server Error in '/' Application.

---

Object reference not set to an instance of an object.

[NullReferenceException: Object reference not set to an instance of an object.]
   DotNetNuke.Security.Membership.AspNetMembershipProvider.UpdateUserMembership(UserInfo user) +57
   DotNetNuke.Security.Membership.AspNetMembershipProvider.UpdateUser(UserInfo user) +201
   DotNetNuke.Entities.Users.UserController.UpdateUser(Int32 portalId, UserInfo objUser) +21
   DotNetNuke.Authentication.ActiveDirectory.AuthenticationController.SynchronizeRoles(String LoggedOnUserName, Int32 intUserID) +98
   DotNetNuke.Authentication.ActiveDirectory.AuthenticationController.AuthenticationLogon() +226
   DotNetNuke.Authentication.ActiveDirectory.WindowsSignin.Page_Init(Object sender, EventArgs e) +102
   System.Web.UI.Control.OnInit(EventArgs e) +2117356
   System.Web.UI.Page.OnInit(EventArgs e) +9
   System.Web.UI.Control.InitRecursive(Control namingContainer) +321
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +692

I removed the role synchronization on all child portals as I have no settings dependent on AD roles in my child portals.  This seemes to have fixed the problem and may confirm the theory that it was something missing in the profile.  For those on a similar path, (always backup prior) the setting is in the update modulesettings table set settingValue = 'False' where settingName like '%synch%'