The server principal is not able to access the database under the current security context in SQL Server MS 2012

Check to see if your user is mapped to the DB you are trying to log into.

We had the same error deploying a report to SSRS in our PROD environment. It was found the problem could even be reproduced with a “use ” statement. The solution was to re-sync the user's GUID account reference with the database in question (i.e., using "sp_change_users_login" like you would after restoring a db). A stock (cursor driven) script to re-sync all accounts is attached:

USE <your database>GO-------- Reset SQL user account guids ---------------------DECLARE @UserName nvarchar(255) DECLARE orphanuser_cur cursor for       SELECT UserName = su.name       FROM sysusers su      JOIN sys.server_principals sp ON sp.name = su.name      WHERE issqluser = 1 AND            (su.sid IS NOT NULL AND su.sid <> 0x0) AND            suser_sname(su.sid) is null       ORDER BY su.name OPEN orphanuser_cur FETCH NEXT FROM orphanuser_cur INTO @UserName WHILE (@@fetch_status = 0)BEGIN --PRINT @UserName + ' user name being resynced' exec sp_change_users_login 'Update_one', @UserName, @UserName FETCH NEXT FROM orphanuser_cur INTO @UserName END CLOSE orphanuser_cur DEALLOCATE orphanuser_cur

I spent quite a while wrestling with this problem and then I realized I was making a simple mistake in the fact that I had forgotten which particular database I was targeting my connection to. I was using the standard SQL Server connection window to enter the credentials:

I had to check the Connection Properties tab to verify that I was choosing the correct database to connect to. I had accidentally left the Connect to database option here set to a selection from a previous session. This is why I was unable to connect to the database I thought I was trying to connect to.

Note that you need to click the Options >> button in order for the Connection Properties and other tabs to show up.