SSAS Cube Not Refreshing Published Reports

Hi Experts

My Power BI Reports are conecting to a SSAS Cube - i am a Admin in Security and also a Admin to the following Group

Groups 

1. HOSPITAL\Oranges

2. HOSPITAL\Apples.

4. HOSPITAL\powerbi.services

My Power BI User: [email protected] and my Domain User: [email protected]

now here is the issue

1. The Dataset refreshes within Power BI Servcies within the Workspace

2.  The Reports do not Refresh and I get the following error message "This reports couldn't access the data source"
3. I have gone into the Settings within the Datasource and updated the EffectiveUserName (i could have made an error here not sure)

4. I have full control on the Power BI Gateway

5. I also tried connecting to the Power BI Dataset and in order to create a simple table and then Publish that report and see if the report refreshed and NO LUCK.

I am totally lost as to why the Dataset updates and the Published Power BI Reports do not.

I have read on line the changing the following setting might help not sure what this means
"The service "SQL Server Analysis Services (MSSQLSERVER)" was running under the default user "NT Service\MSSQLServerOLAPService". Changing the service user to a domain service user (e.g. domain\svssas) "