Hi. Please post the results of completing step 5 in the documentation you mention:
Log on with the user account to the host where the SAS server is running, and use the native database client to connect to the database. If this fails, confirm the user account has file system privileges to the database client binaries and libraries.
This step will remove SAS from the picture and enable to verify all of the MS SQL information is correct.
Next I would run the SAS code directly without involving any metadata stored credentials. Once these two are working I then define the library in metadata and would use the auth domain and metadata-stored user id and password to validate the library.