Robert, it could be a couple of things.
One simple thing that would cause the publishing to fail is if the server did not have the storage capacity for whatever you are trying to publish. This has happened to me with very large datasets.
Another thing is the Server URL, have you published before to this ArcGIS Server connection? I know you mentioned Portal but Server is usually the GIS Server connection with Portal being where content is shared, managed, and viewed? If this is a new ArcGIS Server connection check the Server URL in the Connection Properties, if it has the port in the URL, try dropping the port, saving the connection then republishing.
Example with port
http://houexap95:6080/arcgis/admin
Example without port
http://houexap95/arcgis/admin