Are you the owner of this report?
Please check whether the gateway is online. If it is offline, you will see below error message, and it will fail to refresh dataset.
Also, please check the data source connection. Make sure the gateway can connect to SSAS successfully.
Can you refresh dataset manually on desktop successfully?
Even I am facing the same issue. My gateway is online and its able to connect to SSAS cube successfully. Even from power bi desktop, dashboard shows data but after publising to report server it shows error.
Please help somebody.