Error: The following error may occur while running Form 104001 (Upgrade - Old version) in the process of upgrading from NAV2009 to NAV2013/2015.
The Temp Windows Login already exists.
Problem Statement: If users from other domain exist in windows login table with SID and not on Active directory then the above error will raise.
Generally it happens when we copy customer database to local environment (not in customer domain) and try to upgrade.
Solution: Delete all those out of domain users with SID.