Ok, I see your problem.

The login was mapped to the database as the dbo, which is wrong. It happened because this account actually created a database during the installation.

Please run the script against your database:

sp_changedbowner 'sa'

Then just re-map your login DomainName\Sharepoint-Services to the database (double click on the login->User Mapping->check your DB->check Datareader/Datawriter->Ok)