I am trying to complete the Installation Checklist in order to Configure Platform Server settings with the Configuration Tool, Platform Database, but I am getting an error stating "Failed to grant Admin permissions to user 'sa' on catalog 'Outsystems'".
the user sa has been set has the owner of the DB and and provided all the credentials available.
The checklist configuration I am using is First Install + (Deployment Controller Servers + Front-end Servers + Database) + Standalone + 

Microsoft Windows Server 2008 R2 (64 bit editions) + 

SQL Server Authentication with username and password in connection strings.
Thank you for helping,

I would not advise to use the SA account to be used as the Outsystems Admin user. It should work but that user has much more rights then needed. Can't give you the reason why it fails in your situation, need more info for that. However, try the following. Don't create SQL users and just use new accounts in the Configuration tool, like OSAdmin for the admin user and OSRuntime for the runtime user. Then press the Grant permission button, wait for it and it should ask you to login with an account with enough rights to grant this. For example the SA account or any other admin account that you have. From there you should be able to follow the rest of the steps provided by the manual