Scheduled Refresh Problem for MS Excel Files ( on Power BI Service )

Good Afternoon

I have created a Dashboard using SQL Server Tables and Excel files as the data sources. It refreshes fine in the Desktop environment, and after publishing it the data updates appear fine too. However, when I created a Scheduled Refresh in the Power BI Service, I get the following error pertaining specifically to the Excel file(s) being used:

Data source error: {"error":{"code":"DM_GWPipeline_Gateway_MashupDataAccessError","pbi.error":{"code":"DM_GWPipeline_Gateway_MashupDataAccessError","parameters":{},"details":[{"code":"DM_ErrorDetailNameCode_UnderlyingErrorCode","detail":{"type":1,"value":"-2147467259"}},{"code":"DM_ErrorDetailNameCode_UnderlyingErrorMessage","detail":{"type":1,"value":"Access to the path '.xlsx' is denied."}},{"code":"DM_ErrorDetailNameCode_UnderlyingHResult","detail":{"type":1,"value":"-2147467259"}},{"code":"Microsoft.Data.Mashup.ValueError.Detail","detail":{"type":1,"value .xlsx"}},{"code":"Microsoft.Data.Mashup.ValueError.Reason","detail":{"type":1,"value":"DataSource.Error"}}],"exceptionCulprit":1}}} Table.

Cluster URI: WABI-UK-SOUTH-redirect.analysis.windows.net

Activity ID: a3eaca7b-ef71-41b0-8218-caf902b96255

Request ID: 3d2c84e9-c8d2-85d4-0679-f79946b8499d

Time: 2023-03-01 11:21:12Z

I attempted to change the Permissions (Organizational/Private) in both the Desktop and the Power BI Service (so that the level of Permissions for the Excel file in the Desktop corresponds to what it is in the Power BI Service). However, after actioning this another identical error for another Excel file appeared (and then I resolved this in the same manner).  Subsequently, the same message appeared one-at-a-time for the rest of the Excel files. After modifying the Permissions for all the Excel files, and trying  to Refesh again, the Cycle of error messages commence again (as if the earlier modifications had made no difference).   

I tried the process above twice: first time by making all the Excel Files, Organizational level, and when that was unsuccessful by making them all Private level.

Kindly advise

Regards