Sql-server – How to properly re-add a windows administrator user to SQL Server

The login of the session where you try to set permissions must have permissions.

So, the login you are using is a local admin? This means the local admin group does not have enough rights.

The GUI will run this too sp_addsrvrolemember. Although this says

Requires membership in the role to which the new member is being added.

So, the local admin group is not a member of sysadmin.

Edit:

To solve: Use a login that has rights. you can find one using sp_helpsrvrolemember

The problem is related to the encryption warning but that is not the cause of the failure. When you encrypt with a user key then only that user can decrypt the password in the connection string, otherwise the connection string will have no password. When you don't save sensitive data the password will not be stored in the connection string so you need to set up an SSIS configuration to supply the proper connection string. Open the package and select SSIS, Package Configurations. In the next screen you will select new and then create an XML based configuration file. When asked which properties you want to configure select the connectionstring property of your oracle connection manager and create the dtsConfig file somewhere on your file system. After you create the file and the configuration you can remove it since you may not want the package to look in the same path for the file.

Edit the dtsConfig file and add the password to the connectionstring and then save the file. Put the file where you want it to live and then go into thte properties of the job step that runs the SSIS package. Select the configurations tab and then browse to the dtsConfig file. This should apply the configuration at runtime and the error about the null password should go away and be be replaced by either a different error or it will work.