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Hosts password history settings in Membership Management settings are used with Windows Login (ADS authentication).
There are Page Load Exceptions in DNN 7.1 when DNN tries to add a record to the PasswordHistory table and the ADS user can not log in via WIndows Login.
InnerException: Cannot insert the value NULL into column 'UserID', table 'DotNetNuke_DEHENSV500.dbo.PasswordHistory'; column does not allow nulls. INSERT fails. The statement has been terminated.
I think password history should be ignored when using Windows Login. I had to switch off password history to fix this.
And 2nd when user "SampleUser" logs in via Windows Login using only the UserName "SampleUser" (with default domain defdomain) and logs in via defdomain\SampleUser DNN creates 2 separate users for this, but there should only be one created.