The login already has an account under a different user name.

Details: Written by: Stanko Milosev; Category: MS SQL; Published: 11 February 2013; Last Updated: 04 July 2013; Hits: 8684

If you receive error like:

The login already has an account under a different user name. (Microsoft SQL Server, Error: 15063)

Then just take databse offline and back online. Frome here.