Shaun pointed out to me tonight that a small change was done in the DNNMembershipModule.vb file for 4.5.1 that would force a logout if the currently cached user object didn't match the user in the hard auth cookie.

Basically the chunk of code looks like this:

objUser.Username <> Context.User.Identity.Name  looks like it's causing the problem. If you have any programming background you'll know that when you compare strings the following strings are not the same (domain\username and DOMAIN\username) even though at a glance you don't even notice the difference. In my test install that was having the problem the username was in the database as domain\username which is how objUser.Username was returning it but Context.User.Identity.Name was returning DOMAIN\username which the correct pre-Windows 2000 standard.

So what I need those of you that are having problems to do is to check the Users table in the database and see what case the domain name is. My guess is that it's in lowercase. If you could pick a few user accounts that you know are having problems (and can check to see if this fix works) and change the domain case from lower to upper (or vice versa) . If you could post back here once you tested a few accounts it would be greatly appreciated.

Definitely a case where the string should be changed to all upper or lower case before comparison...

I'll test it out with manual login...

How do you mean at a module level Dan?

Shaun has already applied a fix (http://support.dotnetnuke.com/issue/ViewIssue.aspx?ID=5829) to the offending code that changes the highlighted line of code above to the following objUser.Username.ToLower <> Context.User.Identity.Name.ToLower which will force both to lower case and will solve the problem no matter how the domain or username is entered. It'll be part of the 4.5.4 stabilization release.