Recently, we have had to move some customers from CRM 2011 Online to CRM 2011 On Premise. It turns out the upgrade was failing around the mapping users. It turns out that the CRM 2011 Online uses a field called Windowsliveid. This is basically used in place of the domain\login fields that are used on premise. Having them together causes the upgrade to fail.
So, we need fix this via SQL update the organization before importing it into CRM 2011. From SQL Management Studio, open the CRM Organization database, and click new query. You can select from the systemuser base and scroll over to see the windowslive ID is populated or not. We can now replace that field with a null as it would be for a standard CRM 2011 On Premise Implementation following the syntax below. Now
proceed with your import of your database.
Please review my blog for dealing with removing Enterprise SQL Server Audit controls from the Database as well if you have importing to a standard SQL Server. Microsoft has since updated the request form to indicate what version of SQL you are migrating to, to avoid this issue in the future. Enjoy!