Diagnosing the problem – User cannot logon after a migration

Overview

During a migration, you may get the scenario where the user account has not been migrated fully or where both accounts have been added to the same site collection.

In this case simple remove both user names from the site collection and re-add the correct username.  This can be onerous if complex permissions are involved.

Steps:

1. Go to Site Settings –> People and Groups –> All People.
2. Remove the Duplicate Users.
3. Add the correct username.