Hi,
At a customer we have had a Power BI report since august 2016 with no issues with the scheduled refresh. Of course there has been made changes and improvements since, but the last changes was made on February 21st 2018, but suddenly starting on April 3rd 2018 we can no longer schedule the refresh from the Power BI site - no changes was made to the Gateway or data sources prior to error. We get this error when trying to setup the schedule "You can't schedule refresh for this dataset because one or more sources currently don't support refresh." We can update the model manually through Power BI desktop and publish it to the service.
The report uses 2 data sources, both on-premise SQL databases from the same SQL server.
In the process of trying to fix this we have updated the Gateway to the newest current version (14.16.6650.1 march 2018) and update Power BI desktop (2.57.5068.501 april 2018) and then refreshed the data in Power BI Desktop before publishing it to the service, but neither has helped?