For Database Connectors for MSSQL to be able to communicate with the SQL Server, you must supply a valid user login that has access to the database that you are reading from and writing to. The user login must also have write access to the database in which you installed the stored procedures earlier.
You can set up either one general user login for all Database Connectors users or a login for each individual user. To set up a user login, you must have DBA privileges for the SQL Server; see the Microsoft SQL Server documentation for more information on setting up user logins.