How to create new users for restored databases? I am not too familiar with SQL Server and am facing the following problem: The server was freshly installed and the only existing login is sa.

Then a couple of databases were restored from earlier backups.

Now I'd like to run a few SQL scripts that create new users for these databases, running as sa, but am getting the message that I am not allowed to do this.
The thing you're trying to fix is what's known as "Orphaned Users" - I blogged about this a while ago, at http://thelonedba.wordpress.com/2013/02/22/restoring-into-a-different-environment-security-problem-orphaned-users/

However, without seeing your exact error message, it's hard to help you with specifics.